Contract cancellation

Last year December I sent an e-mail to Altech Nestar informing them that I am cancelling my contract with them to my surprise, January this year I got a statement indicating that my account was over due. I called them yesterday to probe why my account is still active, I was told that they never received my e-mail. I spoke to a gentleman by the name of Stanley Goliath who requested that I forward the e-mail to him that I sent last year which I did. I am really disappointed by their incompetency and unfortunately I have not received any feed back from Altech Nestar until now and I fear that they will continue to bill me for a service that I am no longer happy with.