Cellphone insurance

I had a 36 months contract with MTN ,my phone got lost last week,I reported it then I got an email that my insurance was cancelled due to an upgrade done in August which is a lie I never made any upgrade,today I made a follow up they tell me there’s nothing I can do the sms was sent that my insurance was cancelled,who made that upgrade or cancelled without my concern,who called them to cancel the insurance?they tell me they don’t know but there’s nothing they can do or I can do