Mtn persistent marketing calls

I do not have any business whatsoever with mtn. I do not have any desire to be in business with mtn now or in the near future. However the sales department have my telkom numbers and I don't know where they got my numbers from. I answered their call to tell them am not interested but today alone I recieved 15 different calls, I block them and they come with new numbers. Am working they are disturbing me and anxiety levels are very high.

I need mtn to stop calling my number immediately. Remove my number *** from your system or else I will have to take the legal route for all this emotional distress.