*****ing money from my account

i upgraded my cell phone with Telkom mobile in Eastgate in December 2014 , the phone they gave me was faulty , I returned it within 3 days , they didn't have the phone I wanted so they said they will cancel the upgrade and the phone and wait to do it again when the phone I want comes in. Well let me tell how theses people behave , even now which is May 2015 they are still billing me for a phone and contract I DONT have , every month. They now tell me the number had been moved to a prepaid number as it was cancelled , so why are they still billing me. When I phone they say that it was too late to cancel the debit order for that month , such nonsense as they have been billing me for 5 months now and taking money from my account with no authority .