MTN *****ING AIRTIME JUST AFTER YOU LOAD IT

Mtn is *****s my airtime just after you load which is wrong and they say the system charged you. I just bought it. On the 8th of April 2018 I put airtime into my account and it disappeared I thought some used my phone and then today 18th April 2018 (today) I put airtime of 45rands and the next things my balance 44.59rands. When I called the call centre I was told the system say it was a internet charge and the operate told me that the system says so. I bought the airtime with my data switched off since I was using a wifi connection all day. The system *****s airtime and reports it as internet charge even with mobile data switched off..... Plus we mtn since we have contracts maybe it's time to look elsewhere