Unwarrented PSD call charges

MTN...I have been a loyal contract holder for several years now. Last year May, I renewed my contract. My contract was capped...if my data bundle was running low, I would receive a text to let me know. If I had reached my limit, I would get another text. This all stopped in April this year. In May, I started being charged for PSD calls. I have reviewed my itemized billing. Many of the charges were times and days when I most definitely was in a wifi zone. I have even switched my cellular data off and am still being charged! I have logged my complaint with my nearest MTN branch, they assured me that someone would contact me in 2-48 hours...48 hours later still nothing. I have tried to call you 808 number, but the call gets cut. I called the regional branch and they also promised that someone would call. Nothing. I have made numerous complaints on Facebook (I am most definitely not the only unsatisfied customer, and we are all being ignored), and the only response that I get is that I am using too much data. I am only out of a wifi zone for the 20 minutes that I spend in my car on the way to and from work! I think that I deserve a very quick response.