Airtel — Bill still being generated after disconnection

2 months back I have cleared all my postpaid bills and got the number disconnected since it was lost. I went to the store they told me to request it online. I made the customer care executive do it. Still they are generating the bills and calling me to pay the bills. How do I get a solution?? Now my bill is 1500. I don't want to pay anything else since this is not my mistake.