CANNOT CANCEL CONTRACT!

cancelled my contract with a letter on the 20th of October last year already and requested them to move me over to prepaid. To date they are still debiting my account for the contract. I spoke to a lady about a month ago who assured me that it was cancelled now and that all the monies they had debited from my account would be refunded. Since then nothing has happened again. I have mailed multiple times and now the rententions e-mail just bounces. I submitted my cancellation in writing as they require (even though you cannot find anywhere to mail this to from their website). So legally this is now theft.