Airtel — false information about service

In june 2017, i got a call from airtel regarding hello tune service. They offered me a package of 200 rs. For one year in which i can set 5 hello tune simultaneously and can change anytime for that period of one year without charging a single penny. I informed them that i am going to convert from postpaid to prepaid so i ain't interested. But they told me that it will not affected because of this, it will remain for one year irrespective of conversion so i opted the plan. But when i convert from postpaid to prepaid they stopped the service on the ground of conversion and they refused to help me in this matter.
Is that the way to serve your customer? I got nothing even after paying 200 rs plus service tax. They cheated me and none is interested in helping me.
It is how airtel lost its valuable customer and trust of its customer.