Im not sure whether my sons email gave any explanation of why he was sending it, so its possible it was ignored.
The letter asks for a response at the end asking what happened from his point of view, and must be given in writing. Am I able to do this on his behalf as he is in Manchester and the letter is in Brighton?
Common sense suggests it needs to have a reference number (if there was one, I'm sure these will be now) and a brief explanation. Think what would be likely to happen if someone in an office simply saw an e-mail with a pic of a railcard attached - they don't even include an address - your son may have the same name as another person whose case is being looked into.
You can only write n his behalf if he gives you signed letter of authority giving you permission to do so that you then share with the railway. I'd suggest it would be simpler for you to draft his reply, send it to him (post or e-mail), and get him to send it to the railway.
Keep it brief, clear and concise (all skills he should have if he has secured a place at university....), post the draft here if you would like any feedback or comment on what you have included.
Do this ASAP as you need to prevent 'the computer' putting this on a trajectory to court that will take a lot more time and money to untangle.
(BTW - people at universities - and maybe elsewhere - know all this as 'helicopter parenting'
Good luck with sorting this out. Hopefully your son will have learned some useful life lessons in this saga.