MTN deducting from my account for which I did not sign for!!

MTN has been deducting R1700 from my account per month, the contract that I signed for was supposed to be R1000 per month. MTN has informed me that the additional amount comes from a promotion that I DID NOT SIGN FOR! I contacted them on the 20th of May 2020 and was given a reference number, and they have still not contacted me! Yet they deducted R1700 again from my account on the 30th of May 2020.

This is shocking!