Airtel — not able to do recharge after converting from postpaid to prepaid from long time

I have converted my numer ([protected]) from postpaid to prepaid 1 weeks before, but after that i am not able to recharge. I visited airtel store many times may be more than 10 times. Everytime airtel person s are saying they are sending email to their respective team but why they are not resolving he is also not aware.
I am totally helpless. Since i am using this number since years so i can't change this number also. I cannot believe that airtel is providing so cheap service.
Please look into this in priority.