Incorrect Debit of account

Good day

I called in today regarding he over debit of my account. Normally my debt order is fixed at R1386.73 every month. This month my debit order fluctuated to R1735.66. I was advised on the phone by Andile Bholuliqwe that I received an sms form MTN which said my usage limit is to be increased to R500 and because i did not reply Yes or NO to the SMS, you guys AUTOMATICALLY increase it. First of all, I do not recall receiving this sms, If i do not check my messages , you guys will automatically make decisions for me? I checked my usage and it is set to R1. I do not understand how you guys operate. What do I have to do to receive a refund from my account because you cannot make decisions for me. Never has my usage limit been increased by myself as i did not know how to.

Your prompt response will be highly appreciated