Airtel — regarding issuing my old mob. no. [protected]

My old postpaid mobile no. [protected] has been alloted to network component pvt. Ltd. Pune. As per my knowledge the services on this no. Barred due to non-payment of outstanding bills after the follow up of airtel recovery team we have lodge a complent in airtel regarding a issue. When the issue of the bills are in conversational phase. Airtel alot my number to other person without informing me. It is not the professional act.
As i communicate with mr. Gokhale (Network component pvt. Ltd.) he is ready to return back the mobile number with some conditions. He told me that he want a authorised letter from airtel that the number has been alloted to the firm by mistakely.