MTN's Black Friday deal *******

I renewed my data contract last year and took up the 50gig per month Black Friday special at R299 per month. I have not received 50gig for any of the months of the contract I complained Every month since November but still each and every month I only receive 42gig. I call the help line , I went into several stores to lodge queries but still this month I once again only received 42gig. I am gatvol now I am paying for a service I am not getting