MTN contract nightmare

I have a monthly contract with MTN and they debited me more than the amount on my invoice..I called in yesterday to enquire and was told they will escalate. Today I get the below sms Y’ello! Thanks for using MTN. Your request with ref no *** has been completed. Get 1GB FREE monthly on Ayoba: https://i.ayo.ba/dQjW/iscc

Been trying to call the whole day to no avail, you get to listen to that voice recording for over an hour, only this evening I get through to a consultant and she tells me that I will have to call the credit department for answers…why am I not being called back with an explanation? Why do I always have to call in for a follow up explaining my problem? The service is bad and would not recommend anyone to take out a contract with MTN.