Changing of debit order leads to suspension of lin

I went to the MTN shop in central ave Klerksdorp to change my debit order date, they don't know how to do it. Then I went to the shop in Matlosana mall and they said they have changed it from the first to the 15th. On the first of march they tried to deduct it, resulting it being returned and leaving me with bank costs. The on the 15th they did a double deduction resulting it being returned again, again bank charges. I have then went to pay it at the store and they said it cant be done it needs to go off via direct debit and that it would go off double in April. I went on holiday and the next moment my line was suspended incoming and outgoing calls. after I tried for several hours I eventually got through and they said that it will be deducted on the 15th of April. On the 17th I went to the MTN store and asked why it haven't been deducted and they couldn't answer me. now my line is suspended and I cant get trough to any one. I have been with MTN for over 5 years now and trying to change my debit order date has resulted in me having bank charges and a bad credit report. I cant believe they are so *********** and would not recommend any one to make use of them.