Ridiculous charges on expired cellphone contract

Good day

Telkom is charging me ridiculously after my cellphone contract expired and they switched my account to month to month package automatically without my consent. Whenever I call them to seek reasons the consultants are not willing to assist to reduce the fees.

I explained to them that I do not want the debit order option they refused to cancel it, so I did it with the bank but still they charge a heavy penalty fee when the debit order bounce.

I tried to negotiate with them still they refused and now it is difficult to cancel the contract because I cannot afford the heavy charges against me.

Their service is not good and I am charged almost a double

I need assistance in that regard