Pep cell online purchase

I bought a phone online at pep. So I wanted to make an exchange immediately. So I emailed them they say I can't make changes or request refund cause it's online. But why can't I make any changes on my purchase cause they haven't processed the the parcel. I feel it's so unfair how they treat thier online customers. The parcel is still with them but they can't help me. I feel so disappointed with their policy and how they treat thier customers. Especially online.