Data contract with Mtn

Hello I have have signed up a contract with Mtn last year on the 27/08/2019. It was on a special of 80 gig per month. It has been over four months they have been sending 50 gig and today they gave me 40gig. What they do is that they credit me with 85gig and re-subscribe with 30gig. I have send them several emails regarding this but they never resolved the issue. They have been sending me from pillar to post. Please help me with this issue.Tired of Mtn *****ing my data.