The staff cant change debit date

It keeps getting worse. Since july last year i have been trying to change payment date from the 31st to the 25th. Each time i get told its done only for the 25th to come n no debit goes off. Then i will call again. Saturday i called n i was told it can only be changed in March. I asked to speak to a manager i was put on hold for ever until they cut the call. Wat ******* n nonsense is this for over 10 yrs i recieved terrible service from mtn n the worst is them not wanting me to pay the bill. There will be no money in my account on the 31st. The *****s n idiots that cant change dates that is not my problem anymore. Enough is enough with the mtn bad service