I purchased a dress at The Space and later tried to return/ exchange it

I purchased a dress at The Space and later tried to return/ exchange it. The first reason I was given was that items purchased through Pay just Now cannot be returned. When I went back, I was told the dress could not be exchanged because it had allegedly been altered. So they can’t do an exchange for the dress. I’m concerned because I received two different explanations for the refusal. As a customer, I simply want a clear and consistent explanation of the store’s return policy