Micromax
Imei not found

I have bought a micromax mobile phone and i had connection of airtel before 10 months.

now i have recieved a message from airtel customer care that my imei num is not valid.

my phones services will be rejected on 30 nov. i have the bill of my handset. i think this is the problem of manufacturer.

so please email me how the problem will be solved and what are the details of phone i will have to submit and how??