Airtel — deactivate postpaid number

I bought airtel number [protected] data sim last year but now for the last 3 to 4 months i am not using this.
But everytime a bill of about 1500 is generated and customer care people are calling and forcing me to pay the bill even when i have not used it.

In the month of January also i was forced to pay around 800 rupees saying that after this we will deactivate your sim and no more bills will be made.But nothing of that sort happened and again now a bill of 1500 rupees is made.

I will not pay any amount now further.

Stop your customer care from calling and troubling me.
You cab deactivate this sim.