Horrible service

I have been sending emails to mtn to advise then I have not been working since convid 19.I called the 135 number several times and it does not take me to a consultant to make arrangements. There went a.debited my account and left me on negative. Whose gonna curter for that unpaid debit order.This is not fair. I have informed other service providers not to debit and there didn't. Whose pay for that negative balance