Airtel — porting number from postpaid to prepaid

I have been made to run from pillar to post since last 1 month to port my airtel mumbai postpaid to prepaid and each time lame excuses are given to avoid attending to my request. It seems the company does not want to forgo the benefits received in the form of service tax @18% (Amounting to around rs. 200 pm.in my postpaid plan of 499). It is illogical to stick to postpaid plans when better and more economical benefits are available in prepaid plans.
The customer service is very poor and it compels to give a bad review to my friends and relatives to take airtel connection.
I have been a customer of airtel since around 9 years and had great regard for the good services offered by it. But, it is a matter of great regret that in the rat race of mobile service providers to hold the customers the ultimate sufferer is the consumer of such services. Of late the service quality has degraded and the on time attendance and resolution of customer complaints remains a myth.