But what you should do first is post all the details here about what happened, along with photos of the paperwork that you were given. There may be a procedural error that means you can appeal the fine and legitimately not pay it.
I suspect that in practical terms, this route isn't available. As
. I gave a wrong name and a wrong address
This means that if the OP wanted to challenge the penalty fare on a technicality, they would have to admit to giving false details - and the only way they could get a reply, even if they won on a technicality, would be by giving their real name and address, which would let the railway follow them up over the false details.
Starting from where the OP is, in my view the best way to avoid paying too much to the railway is
- pay the penalty fare now while the penalty element is £50, before it goes up to £100, and
- in future, always buy the right ticket before getting on the train, and so avoid having to pay any more penalty fares.