MTN - cell phone data usage - something is wrong

for years I have been an MTN client, my cell phone account number is A***, cell number is ***. On my cellphone contract, I get, inter alia, 500MB data, 200sms. On 10 Sept I ran out of data, so went to the MTN store at the paddocks and purchased another 500MB. On 10 October, again I ran out of data, so I went back to MTN at the Paddocks and bought another 500MB. when at the store on 10 October, I asked for my account to be queried as to where all the data and sms costs were going, I was told not to expect any feedback Friday, and the staff don't really work then, but I was promised feedback by Monday 12 October. today is 17 October, and I have heard absolutely nothing. I need to know what is using my data, and if it has been **********ly used, I want to be paid back and this issue investigated