Account suspended

I have been a with MTN for 6 Years of which my contract was with Nashua Mobile, when nashua switched our accounts to MTN direct the services have been poor. My number has been suspended for 2 Months now ,due to unpaid debits. I switched my debit order dates from the 15 to 01 of the month dated 18/06/2015 I even got an sms to confirm the debit order dates,on the 23/06/2015 there was an unpaid on my account ,I can agree that no fund were available in my account.On the 10/07/2015 I paid cash an amount of R618.00 ,My services were lifted afterwards,then again MTN debited R708.80 in my account ,now why did MTN debit on the specified (15 of each month) where I changed the debit order to be on the 01 of each month????on the 15/08/2015 there was an unpaid(R427.08) debit in my account ,again WHY did MTN debit on the 15 AGAIN.On the 15/09/2015 got an sms that my services will be permanently suspended if I don't pay the specified amount of R1376.11,since that date till today my I can't use my cellphone or my number, I have my banking on the number.Today I received a statement to say now Im owing R2388.71.I need an explanation why did my account go from R427 to R1376.11.