swear the terms changed after i'd opted in

Opted into an offer last week, went back to check something today and I'm sure the terms read differently to when I joined. Am I losing it or do sites actually do this?

You're not losing it — terms can be updated, and unless you saved a copy you've no leg to stand on. Screenshot everything at the point you opt in, every time, no exceptions.

Seconded. And if you genuinely think they've moved the goalposts mid-offer, put it in writing to support and take it down their formal complaints route if they fob you off. Paper trail is everything.

Screenshot habit starts today then. Ta both — at least I know I'm not going mad.