You'll just have to put up with this for 10 days or so, after which time, your correct profile and speeds will have been negotiated. I doubt that there's an ISP out there who would seriously consider any action until at least then.
Two things to remember:
ADSL MAX is an
up to 8M service.
A new connection undergoes a 10 day "training period" where the eventual connection speed is negotiated according to line etc conditions.
If you go much more than 10 days at 2M, come back and post your line stats along with, and this is important, the
full results including the IP Profile figure of the
BT Speed Test.