Airtel Prepaid — cancelled the number

Hii,
this is Niket Zaveri.
I was buy a new airtel prepaid connection last year with 1 year validity.
After that I was going out station for personal reason.
Now I am Coming back and start my sim card so its not working.
After that I am calling to Airtel customer care then they ask methat you are not use this card for three month and then your card will be cancelled.
What's this???
Now Airtel go down to this level cheating??
because I was paid for 1 year rental. and that time they are not ask me that things.
They get full rental and not giving service??
Is in india customer is important? and where is the authority body who undertake this??
I cant understand that things.
I am proud to my India but how can this proud??
Hope getting satisfaction.
Regards.
Niket Zaveri
[protected]@yahoo.co.uk