Charged R1180 for R199 package I signed for

Hi, I have been trying to communicate with MTN for weeks now. I signed for a contract 26/11/17. On the 4/12/17 the number ported. I loaded the MTN app only to see a bill of R1182, the contract I signed for was R199. How is this even possible??? My first message sent to MTN was rep**** to two weeks late. I was told someone will contact me, no one has. They just stopped replying on messenger? I am in a position now where I am being charged 10 times the amount I signed for and no one will assist me in this regard????? How can I a business do this? All I want is what i signed for. Why does MTN not get back to me in this regard???