Bad service

I took a contract of sim only deal 15g for R149 with mtn on the 1ths of August, the told me that I will be paying R149 on the date that I choose when the sim card came it was not 15g it was 5 from this month I have received 3 massages with 3 different amount on what I will be paying month end and it can't be that I over used my data because I still have them