Airtel — changing the name on the sim

I want to change the name on the sim and unable to do it and tried to seatch for customer service number but unable to do it and when went to service centre they said i need to comvert my sim to postpaid what is this airtel is cheating all the customers. Please change my name from vineetha amazon to vineetha and i've all the proofs. Help me how to change the name ad it is very important for me to change the name on the sim. When ever i call others they see my name along with company name so need to change.