MTN ******ion or *****

I paid of the handsets on my contract in February this year and also cancelled two numbers on my contract that I don't use. I also downgraded my plan to a cheaper plan on the 2 existing numbers. MTN is still charging me upwards of R800 per month. Upon enquiry, they told me that I used out-of-bundle data. This is nearly impossible because I use either WIfi or a Vodacom Mifi router and my mobile data is switched off most of the time. Every month I get an exorbitantly inflated bill and if i don't pay my service is suspended. This is *****. I tried to report it but nothing happened.