A lot of these parasitic companies want a quiet life, and they want people who will send them money. They don't want people who argue and are not willing to pay, because they aren't cost effective.
As has already been quite correctly pointed out, things like this are a numbers game. They want the easy targets, the uncontested cases. They can deal with hundreds of easy ones like this per day. Send out enough invoices, and statistically some of them will be paid. But the parasites can deal with far fewer cases where someone makes their life complicated or who writes in and asks upon what basis in law they believe the money is due, because then they have to think, and work, and spend time. Time they could use far more productively on easy cases where people roll over and say, "Oh I'm so frightened of this letter you've sent me with all legal sounding words on it. How much money shall I send you to make all of this go away ?"
It's not just parking scams either. The thing is, these organizations don't know who they're dealing with and many of them, as soon as they get any hint of a situation that's anything but straightforward, will bin the whole thing. I've had various threats of court action from insurance companies and solicitors over many years. But as soon as I've written back and said I would defend any proceedings and claim costs against them, guess what, suddenly they just give up and move onto easier pickings. Sometimes they issue proceedings to see what will happen. If you defend and / or counterclaim, they discontinue and concentrate on the easier targets. It's similar in some ways to any bully you're likely to meet. If you cringe and run away, they chase you. But if you front it out, stand your ground or hit them back, they leave you alone because they want easy targets, and they'll look for someone who doesn't put up a fight because they can make more money that way.
If you dispute something, you should always consider defending county court proceedings. If you represent yourself defending a small claim in the county court, it shouldn't cost you anything to do this . You wouldn't normally be liable for any extra costs the claimant ran up such as their legal representation on the day.
The summons the court sends out is called a Default Summons. This is because if you ignore it, the Claimant will be allowed to apply for a default judgment against you. It's fairly straightforward to defend a county court money claim, and far easier than it is to have to apply for a judgment to be set aside later. I've heard many people say they would just ignore it until they got notified of a hearing date, but if you ignore a default summons, there won't normally be a hearing, unless it's for subsequent enforcement action or unless you want to go to the trouble of applying for the judgment to be set aside.
If you believe a claimant with a questionable case has issued proceedings as a means to intimidate someone into paying, with little or no intention of actually seeing the matter through, or turning up in court on the day, you can sometimes apply for a wasted costs order against them or their solicitor. I often send a standard letter with a copy of the defence pointing out that if the defendant is put to the trouble of preparing the case for court, only for the claimant to discontinue the proceedings before the hearing date, a wasted costs order will be applied for.
I once estimated that for every 100 sets of county court proceedings I issued, 10 were initially defended on paper. 90 defendants would ignore it and I'd obtain a default judgment against them. Of the 10 who put in a paper defence, 6 would hardly constitute a proper defence anyway, and were at best, a list of reasons why the defendant didn't want to pay. The remaining 4 would often be a coherent defence, but of those 4 remaining defended claims, only 2 or 3 defendants would actually turn up on the day of the hearing.
Think of the practicalities of all this. Where is the office based where the proceedings are issued ? (and I mean the office of the company that's chasing you for money, not the court office). Because any defended county court claim against a private individual will automatically be transferred from where it was issued (either Salford or Northampton), to the defendant's local county court. And if the office that issued the claim is on the other side of the country, then someone from there will have to travel to the actual court where the case is to be heard, or they will have to instruct a local solicitor to act as their agent and conduct the case for them on the day. Bear in mind that on the small claims track, which most cases like this will be, each side pays their own costs regardless of who wins. This means that even if a defendant representing themselves loses on the day, they will only have to pay the amount of the claim, plus the fixed costs, but not any of the claimant's costs over and above this, such as the charges for their solicitor appearing on the day. All of this means that you are at an advantage as a litigant in person, and if you make it very clear you won't give up without a fight, there probably won't be a fight, because these parasites just don't have to time to waste on people who actually can be bothered to defend things like this.
Most money claim county court cases don't end up going as far as a court hearing, and because of this, many people have very little if anything to lose by defending claims.
Unless of course you're bang to rights, in which case, just pay it or do a runner to the Ecuadorian embassy, or whatever it is you have to do to evade British justice these days.
** Edited to add - If you do end up with a CCJ, it will only go on the Register of County Court Judgments if it remains unpaid for more than a month. This could then effect your credit rating for 6 years.