MTN replacement device blacklisting

I lost my device, it is a replacement device. I tried to get it blacklisted so I can put in a claim from the MTN insurance however I am being taken back and forth by the consultants saying they cannot see the IMEI number of the device connected to my contact number. I went to the store and I was told to call 135, I am still not receiving help there. I even called MTN insurance to confirm the IMEI number for the replacement device and the number matches the one I have on the box. I am not left without a phone and yet paying for it and insurance. The consultants are very ***********.