ridiculous billing amount

I received a phone from my employer, I hardly ever use the phone for Internet. To my suprize I received an sms stating that my account will be debited R4400 on 25 Dec 2015. I tried several times to phone mtn but it says my services has been suspended. My employer human resources department even send an email to query this but there is just no reply. Even no mtn store can assist me with my query. I even receive an sms that does not make any sense to me at all: Dear customer. Please assist MTN to improve service by answering 6 questions based on your sim swap experience. .. I never even did a sim swap. I am even trying to Google this problem, and I see that a limit needs to be set in order not to get this shock of a bill. What do I do when no one at the call centre can help me, and when the stores send me from pillar to post? I'm am new to MTN and I am not impressed at all. I need answers ASAP. What simswap was done? Why is my account running Internet charges everyday? Why is MTN not answering clients emails.