Day light ******* by MTN

I have taken out a MTN contract through Mondo in June 2021 and one of the two lines were wrongly issued. When I called Mondo in July they acknowledged their fault and promised to cancel the line. I have since then been calling Mondo and they keep telling me that the request has been sent to MTN to effect. My numerous calls to MTN don't bear any results as I either get told that it was in the process or they would just hang up on me while I am talking. I am so regretful of moving to MTN and am disappointed that they bill me for something that I am not using, or which they have not issued.