FIX MTN

My account is being billed for BIS but my contract is for a Samsung, my monthly airtime seems to be disappearing without me using the phone and MTN's excuse was that it is being used as data, but I had data on my phone that they changed the type of. My money is still going missing, round about R10 per day. I mailed them, went to a MTN store and reported it and still nothing has been done. Besides that I get spam sms's daily! I got a rude mail back (eventually) that still didn't address my problem and just asked me to prove that my contract is for a Samsung. This is the worst provider ever and I am going back again today, if it is not fixed I am changing networks!