@hacktrix FYI I am an AA user (and there are one or two more kitizens who are too) and I don't have any usage cap. I pay for what I use and there is no limit of any kind. I just suggested it because people claim that AA is relatively speaking ferocious at fighting with BT on behalf of customers. Some users buy a certain amount of download allowance and then top up if necessary. They have a 1TB download pm pre-purchase deal and there are various other deals. I don't recall all the details.
Also AA used to have a fix your line or your money back deal for people with problems, but I don't know whether that is still going. It doesn't cost anything to talk to them about your problems anyway. They are very approachable and are in IRC, SMS, web-based chat email of course. Only you know if they might be a good fit for you. Their IRC channel is full of other customers as well who are very helpful, not just highly techie staff.