Cellphone insurance not approved

Hi I have a problem with Markhams I bought a cellphone Samsung A30 in August 2019 for my niece with my Foschini account. I insured the cellphone and I'm paying R86 premiums. My niece passed away and her belongings were put in a safe until the ritual be perfomed.When that period ended my sister phoned me and told me that the cellphone was missing from where it was kept. I tried to blacklist the cellphone with MTN they said they can't help me because I dont know the IMEI no.I tried to engage Markhams the shop assistant from Markhams Pritchard n Joubert street Jhb was very helpful but at the end of the day the Customer Service said they can't help me because I took the insurance over the phone and the.person who was assisting me did.not put the IMEI no when he/ she register that insurance .I've been paying that cellphone insurance since September 2019 but they dont want to approve the claim.