SIM ONLY Dtata Contract Cancellation

I hve this other Challenge with MTN Sim Only Contract, that i no longer want it, ive tried to cancel it since last year November and no luck. The open account contracts for us in store but when i have to cancel in the store they ask me to call thir online cancellation servive, they put us on hold and when they get my calls nothing. Make sense the contract continues to deduct my money. I no longer use it anymore it doesn't even give me a good network. I kust need it to be canceled.