Call back, and try and get someone in Swansea - I find the agents there are top notch and know what they're doing first time, every time. You've probably come across some internal policy that the agents follow to try to reduce expenditure, but what you're describing seems to me to be a pretty clear-cut EU/UK261 case. If that doesn't work, then email [email protected]. Look for the flights you want - they should re-book you in to the same (or equivalent) cabin as your original ticket - before you call. If there's no availability, they won't be able to force anything open, even on a DL service. Hope you get it sorted!