8ta / Telkom Mobile
Cancellation of contract

My contract expired four months ago. Nobody phoned me to renew it.
I cancelled the contract and on the 21/9/13 I send them a fax to cancelled it.
No feedback from them so far.
Every month for the past four months the still debit my bank account.
What must I do to stop it?
Regards
A.C.Strauss.