I know its an early start, but theres a 2am coach from Cov (swap in Brum) gets you on site for 7.30 thats £50. Always worth checking what the difference with a coach railcard is (I assume you can get one cause you have a train one) cause it shouldn't be massively expensive.
Most rail companies are allowing refunds on tickets bought over the period so hopefully you can get your £70 back, or the outgoing bit at least, and getting BACK from the festival, even though it might be a bit of a pain, probably isnt as time sensitive for you as making sure you get on site!
If you're really stuck getting back, drop us a DM because we'll be driving back to Brum Monday afternoon although there's a big awning to squeeze your feet around haha