Incorrect data received

I have a contract with MTN. I don't get the same data that is confirmed on an sms I receive monthly. Supposed to get 500 mb but I get 250 mb yet on an sms they confirm that I received 500mb.

It's an inconvenience because my mom is using the number, she can't even recharge her data nor convert her airtime to data. I called the 083 135 number, USELESS. I never get to speak to a consultant.

Can MTN get to the bottom of this as I will be cancelling my contract if this is not resolved. I can be contact on *** (Note it's not the number in question)