Refusing to return security amount

Hi

I have ported my number 7211151888 from idea. I bought this connection 2 years ago and have deposited a security amount of Rs 300.
I have lost my receipt as its too long since i have bought the sim.
Now when i have ported out idea is denying to return my security deposit anount saying that there is no amount reflecting wrt my connection.
I have a copy of mail where idea have reverted me that the amount is reflecting in my account. But now they are denying.

Dont know if they want to built a bunglow with those 300.