autopage keeps billing me for closed accoun

I had a contract with altech autopage which I paid up and requested them to close. Now a year later I am still being billed for that account. Iv tried many times to rectify this with no luck. Now they have sent my account to a debt collection agency and because I dont want a bad record I paid up fully for an amount I dont owe. I called their billing department again and they promised to rectify it and get back to me. Today I still have have not heard from them and I am still being billed. Whats worse is that their call centre never answers calls. Altech, I want my money back. This is seriously frustrating. I am being milked for a contract I dont even have. Can anyone advise on what I can do to put a stop to this and get my money back. The account number with altech is 1.***6