Guys I would like to know by the end of this week how many people think I should reply or not, based on that I will see what to do.
You have a choice. You can follow the advice given by experienced people on this forum, or you can reply to GA and expose yourself to the risk of admitting something that they appear to have no evidence of.
The first option involves sitting tight, seeing some unpleasant letters come in, and having the strength to remain silent. It comes with a small risk (<10%?) that they do have real evidence about your fare dodging and that they use it, but the odds are that they don't have the proof that they would need to take action.
The second option has a very high risk (90%+) that you will provide them with evidence of your fare dodging, and give them the means to (best case) demand a settlement payment from you, probably over £1000, or prosecute you for the criminal offence you have been committing. That will also be expensive, and a criminal conviction will affect you in other ways too.
From your writing style, I suspect that English is not your first language and I will also assume that you have been brought up elsewhere. When considering your choice, it's worth remembering that English law, unlike many other systems, both gives you the right to remain silent and not incriminate yourself, and then protects that right strongly.
As
@jfollows says, this is
not a poll. We do not know the details, we do not know how you make your choices. You need to make that choice - but do so considering the advice you've been given.