i lost my cellphone but cant black list it

i've been a cell c customer for almost 10yrs now but to my horror when i called cell c tryng to black list my phone as it was ****** i was told they cant help me as my phone number doesnt belong to me. how possible is that when i rica twice already, now i have to wait with no feed back from them till i don't know what happens. if i lose out on my insurance because of them thell be hell to pay. how can they say the number doesn't show i'm the owner when i bought the sim and ricad at jabulani mall.i wilol take cell c to the omburdsmen