Impossible to cancel fixed line

<p>I have been trying since October last year to cancel my fixed line phone. I have spoken to the call centre 4 times and send the cancellation form about 5 times with absolutely no result. Every month I am once again billed for this line. Can somebody please tell me what I am supposed to do to get this sorted? And what about the 7 months of line rental that I have been forced to pay even though I don't even use the line and have been trying to cancel it for months!</p>