MISLED SALES UPGRADE

I upgraded my phone & contract after receiving a call from MTN's sales department in June this year. I was assured that this would not cost more, in fact less & that my upgrade package would be similar i.e. 125 mins airtime & 1 GIG data when I actually now have 75 mins airtime & 4 GIGS data. This has resulted in me running out of airtime. I have phoned their call centre 3 times as well as sent several emails requesting a change to my contract as I felt misled but these have been unanswered. This has resulted in me having to buy an additional R100 airtime p.m. that I find untenable & would like a response & some resolution to my problem.