Cell C and MTN are pathetic

On the 1st July 2019 I was the victim of a *******. My phone was ******, a phone i purchased at MTN. I have insurance on the phone and am needing to blacklist the phone before i can claim. However because I use a Cell C sim card as well neither network is able to assist me. Both sim cards are registered on the insurance application however both networks are giving me the run around when it comes to blacklisting. I have contacted the customer service line for both networks and have been into both stores with my cell phone box and copies of all documents and affidavits. When being assisted by MTN im being told the cell c sim card was last used in the phone therefore they cannot assist and i need to go to Cell C. I have taken the box with the IMEI number and still no assistance in blocking the phone. When going to Cell C, i explain that the sim card was a free sim card given at the stations 5 years ago when i was still on school therefore it is not registered on my name and because of that they say they cannot assist me in stores. When calling the customer service i am able to answer all questions except the last dialled numbers. I explain that the cell c sim card was never used for dialling only for data as I receive free minutes on my mtn sim card. But i am able to give all other information. However they are still not able to assist me. So what both networks are actually telling me is that the person that ****** me by knife point can sell my phone or use it as he wants because i never dialled numbers on my cell c sim card. Is this the service that i must receive from cell c and mtn but every month they can deduct their premium off my account for the phone contract and insurance without fail. I am not a ******** but i am being treated as one just to blacklist my phone. Now i get told because none of them can help me the phone will never be blacklisted and i wont be able to claim from my insurance. Golden Acre Cell C and MTN branches. pathetic customer service. I would not recommend these networks to anyone.