Airtel
Message from airtel service stating that my IMEI is invalid

I got a message from airtel service stating that my IMEI is invalid and that i need to get new IMEI from govt approved centres. I purchased my mobile from an authorisd dealer and its been over a year. How can airtel say that my IMEI is invalid!! I would the customer service to sort this out.

My no: 9730541283

IMEI 355556010387597.