Myntra.com — Selling product forcefully

I have put my cash in myntra credit then I buoght some products and because of bad quality I returned some of them. then these myntra people charges convenience fee of 145 rupees extra... that I gave . and now I bought one top and shoes . i have taken shoes but top is of bad quality so first I want toexchange but only size can be exchanged so I tried to return and now they are splitting my money like 1/3 in my account and 2/3 in myntra credit .
what is this?
i am so angry after taking convenience fee ... they are still doing this its like you are selling your products forcefully ... after this i will never do shopping on myntra its just disgraceful ...
please resolve this ...asap