I had a similar problem with Tiscali. I signed on for 1MB 2GB cap last April at £15.99 and was getting up to 2.3MB for the first six weeks.
Then Tiscali realised its error and throttled it back to 1MB. In early August Tiscali upgraded me to 2MB free of charge but, at the end of October, its "service enhancements" saw speeds drop alarmingly.
Tiscali's engineers insisted that my line would not support 2MB (thereby shooting themselves in the foot).
So I dropped back to 1MB unlimited still at £15.99. I then noticed that the true price was £14.99 so did the downgrade on its website.
The result was a 1MB 2GB cap service...:-(
After several abortive attempts to get the unlimited service restored, I finally got an e-mail about 10 days ago to state this had been corrected.
The e-mail also made it obvious that I wasn't the only one to suffer this unnecessary cap as it was addressed in general terms.