Constantly referred to other departments

Good day

I can only guess a sim swop was perhaps done on my wifes number but there is no history of sim swap with Mtn and her number still works.

But what is strange, there is number that appears 20 to 30 times a month on the itemised billing that my wife says she has never called. I have tried calling the number but it comes up as "the number you have dialled does not exist". Is it possible the number has been hacked as it is using minutes and can only think it must be a data sim as I cannot through.

What I am unhappy about is that I have tried calling Mtn multiple times and I just keep getting referred to different departments and nobody can give me the possible explanation of what is happening. I have logged a ticket on the 15 May and was told someone would contact me within 24hr's but unfortunately nothing and today is the 25 May.

I would greatly appreciate some assistance please and thank you.