Inconvenience on incorrect debit order date

I have a contract with MTN and in December 2019 I asked them to change the debit order date to the 1 of every month as I will be getting paid on the last date of the month now. One person said they changed it, And it was nt changed. I called again and another person said they only change it on the 28th, I should try call again on the 28th of that month. So as a customer I am wondering, why are they not noting down that a certain number of customers called and requested a change on the debit order date. I resorted to going to the store, at the store I was assured that it was changed but it wasnt. Today I call them to ask that they please change it as money was still deducted on the 25th and they took money that wasnt mine, now I owe someone money who had trusted me to do her request. The lady, Sibongile told me to call on the 2nd of April, because if they change now they will deduct again on the 1st of April. Sibongile the consultant ask me that is that what I want (them deducting twice) if not I should call on the 2nd of April so that they deduct on the first of May. I am sooo frustrated because I have a feeling that on that day another excuse will come and I will be face with the same challenge