Supersonic poor service

Firstly, i had endless problems with their double billing me, eventually got sorted out after escalating to Calvin Collett. Now 5 months after I cancelled my subscription and settled the last bill in full including clawback they have billed me again for clawback. They did not even bother informing me, only found out after receiving sms from debt collector Nimble. How disingenuous of MTN Supersonic