MTN Falsely Crediting Account With Data

I have had horrible connectivity with MTN, however that goes with their *****ulent behaviour.

I have a contract data sim with them and on the 1st of the month I receive messages that I've been credited with data, however for the past 3 months or so nothing has been credited on my sim card.

I am unable to use their chat services to get assistance.

Assistance in understanding this matter or in cancellation would be appreciated.