Very unhappy customer

So for the past 4 months I've been battling with Mtn regarding my monthly data. On the 21st of January I received an Sms to advise my query has been resolved. By the looks of it, it was never resolved. They keep on taking half of my data every month for the past 4 months. I'm fed up with Mtn and how useless they are. I WANT MY DATA!!!!