Telkom Mobile keeps debiting my account - I don't owe them a cent

Telkom Mobile have been billing for An OBF handset which Telkom Mobile has in their possession. I cannot get assistance from the various stores... Iv called the contact centre countless times. I have some many cases logged with their billing department. Nobody ever gets back to you. Telkom has been billing me different amounts twice monthly as well... This is besides the OBF handset....I don't know what to do anymore .... I've incurred bank charges for all their random debit... please assist