Very poor services

I am very upset with the services at mtn. I notified mtn on the 1st of June 2022 via email that my pay date has changed to the last day of the month and they responded to confirm that the debit date is changed. Now My contract line is closed and I am being told payment went through on the 28th and is rejected and i have to pay approximately R600 to be back online again ( way more than my actual installment)

1st I notified 30 days prior to debit day and now I'm told it only becomes active 30 days turnaround time. I have never been paid or selected debit date on the 28th

I now have to pay for charges I didn't create.