Rescheduling debit date difficult sofar

I once asked for rescheduling debit date after my payday and was told it was impossible and but it does not matter but later was charged additional R70 and received notifications regarding terminating of my data. Last time support confirmed the debit will be on the 6th every month but that didn't happen. If my balance was empty today I would be charged additional R70 next month again.it has been three months in a row now paying an additional R70.00 fee.