Billing account change request ignored

To whom it may concern.

I upgraded my MTN contract in November and in so doing, also changed my debit order banking details from a standard bank account to Absa, I received a statement via sms with the Absa banking details. I called around the 22nd of December to have my debit date changed from the last day of the month to the 25th. The operator highlighted that only the standard bank account is reflecting on her side, I gave her the Absa details as well to update. I received confirmation sms of such an update.

On the 3rd of January the contract bill was deducted from the standard bank account, luckily I had funds in the account though I am not actively using it. May someone please ensure that the correct account is used to debit and done on the date (25th) I requested? Bouncing debits are charged to me and I can not be made to pay because MTN is in ***********, more so when you send statements with correct information but proceed to do the opposite.