MTN just ***** money

This institution are straight-out *******! I had a month-to-month home internet plan with them about a year and a half ago for 400 GB per month. I never ever got my 400 GB, every month it would "run out" after about 330 GB. I then cancelled and got Vodacom which is a million times better - I did everything right, gave 30 days notice, returned the router, no problems. This month, more than a year later, all of a sudden I just get debited with R978.26?? ***??? Never received a statement or account ever again, and now all of a sudden they just take out of my account. What is wrong with these people? I will never ever ever trust or do business with MTN again - they do not deliver what they promise in the first place, and they ***** money just out of your account. I cannot dispute this at the bank, because it was a debit order mandate that I signed more than a year ago (although it is month-to-month) - these people are *******. My subscription that time was R399 per month, so where on earth do they fall out with almost a thousand rand???? These people should get arrested for theft, and MTN should be shut down.