Airtime being ******. No assistance to resolve the problem from MTN SA

My itemised billing statement indicates that I am making calls to a specific number ***) every day 2-3 times a day for the past 6 months, even though I have never called this number or received a call from this number in my life. I logged a complaint about this to MTN over a month ago. They have not to date contacted me, given me feedback or followed up on the logged complaint. While my airtime is being ******, I am not getting any assistance from MTN as service privider.