Their service is very poor

I am freedom muponisi makharinge I have the account with mtn, and I am still paying the device (galaxy note 20 ultra) I did insure my device, I lost my device then I claim the device from mtn insurance, It was approved and I paid the access, it's been three months now they're not giving my device back, when I do the follow up they said they don't have the same device that I insured for, they cover me for R26000 but they are offering me something for R17 000, I need help please.