MTN is horrible

I am so incredibly disappointed by MTN that if I could I would terminate this contract and never ever deal with them again. I changed my banking details and debit order date with MTN via the call centre, they still deducted from the old account and barred my contract as that old account no longer existed. This inconvenience happened for 2 months and then I decided to lodge a complaint with their complaints department after dealing with their rude call centre agents. I was asked to send my new bank details via email, which I sent a bank confirmation letter and was then assured the banking details have been updated. Come December 22 I receive an sms from MTN that my debit was returned unpaid and that they have barred my contract again. I immediately sent an email stating how false those statements are as the account had and still has funds and did not receive a single response, only sms threats that this will negatively impact my credit score bullying me while they are the ones in the wrong. It is unfortunate that they get to breach their contractual agreement to me, but still send me threatening messages and I have no legal leg to stand on, laws need to change.