but to say that Wanadoo's service is a "big swindle" is libel, and I must caution you not to repeat it. I'm quite sure they are not swindling you, but you're obviously having a problem.
There may be reasons beyond Wanadoo's control that are preventing you from receiving a faster broadband service, but the first thing to ask is how you know that your downstream speed is limited to 512Kb - have Wanadoo confirmed that?
How far are you from your local BT exchange?
You say that BT confirm you should be able to get a 2Mb connection - have they done a line test in order to confirm that, or is it just something they said over the phone?