I've seen and heard permission being given, verbally, which I've thought is BOUND to give problems to the person later on. Obviously I've not followed them to see if that was the case.
These 'people on the platform that said it was okay' DO exist. Nowhere near as often as claimed, but once is too many. These people do no favours for the rest of the railway staff, although I am sure they all feel they're being helpful and not considering the potential for problems. Or maybe some are aware, but don't care as long as it gets rid of the person?
And I've been given advice that I believed to be incorrect. But I will never accept verbal permission, for obvious reasons, so I ask for something in writing. In ALL of the situations where I've been suspicious of what I'm told, my request has been refused. I sometimes get the question 'Why do you need that? Don't you believe me?' and still get refused!
It's obviously little comfort to the OP now, but if a member of staff did let him through and give what appeared to be permission to sort things out at the other end, then it would be vital to get that in writing - or on tape/camera. But the chances are, the OP would then find such permission would be retracted very sharpish if a camera or 'tape recorder' pulled out.
In my opinion, the ONLY viable solution is to pay IN FULL right away and then make a complaint to the TOC to recover the money.
DO NOT IN ANY CIRCUMSTANCES TRY AND FIGHT THIS IN COURT!
I'll add the usual disclaimer of 'assuming the facts given here are truthful' first, but there seems to be a valid case for complaint. Had you not been let through, you'd obviously have been stuck but at the same time not get into the situation you are in now. You might have chosen to, say, get a taxi to someone who could give you some money.
Trying to avoid the RPIs was silly, although I suppose I can sympathise about the thought of having to explain to them when you wanted to sort it at the destination, but unless the RPIs knew you were walking away to avoid them - I am not sure they'd know you even did that? And of course, I assume you aren't lying about having made arrangements to have someone meet you to pay (as against try and walk out and not pay at all).
And, finally, if you were so sure your card might still work in another machine, perhaps you can argue that you DID have a means to pay. But perhaps the staff at Tottenham Hale should have advised on other options, such as SILK.
Finally, let me say again - PAY UP and then seek to try and resolve things afterwards.