about my lost mobile handset

Location/place: Rajasthan (Barmer district)

Name of company/service: airtel and samsung mobile

G.M sir,

This is to inform you my samsung corby mobile had been lost before three days i have contact airtel customer car & samsung customer care for block my handset by IMIE no (i have read from internet that service provder can block handset by IMEI no.) but they cannot help me for that.
in my handset mobile theft tracker facility so i have received message from unknown no. 8003671148 (Airtel-Rajasthan region) no. which person have my lost mobile hand set so. pl help me how to get my mobile from this person
pl guide me for the same

Thanks & regards
Hemendra visavadia
99981 59188 (Gujarat)