Strong requests :
I insist that you refund my money.
I feel you should, at the very least, refund the sum I paid.

Polite requests :
I’d like a refund please
Is it possible to have a refund please?

Exchange = When you can change your item for another item of the same price.
Refund = When you receive your money back after a purchase.

Other vocab :
To window shop ⇒ To explore without buying clothes.
To shop around ⇒ To shop in different places.
Impulse shopper ⇒ To buy something without thinking.
To take something back ⇒ To return something.
Rip-off ⇒ Too expensive.
Bargain ⇒ Good value.