Airtel — airtel fraud in postpaid connection

Address: Thane, Maharashtra, 421201

I had taken a postpaid connection from airtel with number [[protected]] in the month of october.
After using the service for a month i went to airtel gallery and asked them to close the connection, but they denied saying that once you start any postpaid connection it cannot be closed for 3 months.
I continued to carry the connection for another two months and paid the bills even if i had not used the connection.
Now after the third month they called up and said that we had suspended your connection, clear the last month bill and close the connection.
When i went to gallery the staff at dombivli (E) gallery [near p p chambers] responded rudely saying they cannot process my payment and will not close the connection. When i went to another gallery they asked for 300inr more than that was communicated to me. Now because they have not closed the connection i will have to pay another month payment.
Please look into the issue urgently.