Deactivate phone without informing anything

Location/place: Pune

Hi,
I am using airtel mobile sim 9766180587 (Maharashtra region-Pune).
But the sim is not functioning and I am unble to know the exact reason.
All other previous bills were paid on time.
Kindly do the needful to resume my phone service. At present I am traveling and facing lots of problem due to this problem.

Regards,

Nilesh Pathare.