MTN poor service

My name is Sinethemba, I’ve been bul**** by MTN. I had a contract with them from March 2022 the in May 2023 I paid off my contract account. I called their customer service and sent them my proof of payment then suddenly almost a year later they decided to debit R3700 on my account saying I have accumulated interest of which is their fault because I’ve been calling them to cancel my account and somebody did not update my account. Worse part is that my MTN services are suspended without any notice.

If there’s anyone who can help me I need contact details to lay my complaint against them.