MTN has NO Customer service at all!

MTN cell phone services! In August 2021 my partner passed away and his MTN contrach was paid monthly with a 'debit order' on my bank account. I visited the Eden Meander branch in George to inform them to please cancell his contract and they wanted a copy of the Death Certificate - no problem! I called his Estate Attorneys and they emailed a copy within minutes - and I have proof of this. However for 18 months after this MTN still charged my bank account with the fees and to date the amount is about R3800 which they stole from me. I ahve been trying since then to get this refunded WITHOUT ANY SUCCESS at all! Their Customer Call center is useless.. I emailed all the details they wanted including a sworn statement by myself with proof of deductions and all the relative information......BUT to date I have been fobbed off and NOTHING has been done. Basically they have stollen these funds form me and refuse to give it back! What can I do?