Unauthorized changes made

I have been an MTN customer for over 10 years. Never any problems. 2 months ago I get an sms to say my debit order was returned I need to make immediate payment. Debit order was put through on the 21st. My deduction date is the 25th as I get paid on the 23rd. Contacted MTN and was assisted. Debit order was restored to 25th. I queried why it was moved and got no response. Last month the same happened again. I called MTN and asked why are they moving my debit order date. Again, no response. I asked the agent to please put the debit order through for 25th as the previous agent had done. I then get an sms to say my debit order will be processed on the 25th but my arrears have been split over 2 months and will be added to my payment. As per my agreement with the agent. I went to an MTN store to query which arrears as my statement shows none and was told they cannot see what the agreement was I made with the agent and that their accounts department is in a mess. This morning another sms received to say 2nd part of arrears will be deducted as per agreement. Again, which agreement? I had asked the agent to correct my deduction date so that my normal payment went through on 25th. I would therefore like to query 1. Why was my debit order date changed from the 25th to the 21st as this request was not made by myself. And 2. I want all the calls between myself and the agents listened to to determine when exactly I agreed for "arrears" to be deducted. There were no arrears and i made no such agreement. You can trace the calls with my cell number. This is ***** and i would appreciate an investigation. Thank you.