Bad experience and failing to resolve my issue with MTN

When you purchase data on MTN momoApp watch out they can turn all your data that you bought with momo to airtime that you don't need as you can get good deal when you are using momo App . Yesterday I cash in R350 on my momo to purchase data after cashing in I bought data for R349 and when I was done they now told me they use my data to pay airtime advance of R13 which I took , and they then turn the remaining balance into airtime which I can use to purchase data on momo , they waited for me to purchase data instead of taking their advance airtime on momo , ns now they don't want to resolve this they are sensing me from pillar to post. I want my money to be credited on momo as that is where it was not airtime.