Poor service truworths Bedford centre

I bought a dress from truworths Bedford centre. The tag is still on. The dress is still in good condition. I don't have an invoice though. I've printed my bank statement. I just want to do an exchange for something else. Consultant was blunt with me, turning me down, saying I must have the invoice. Says Truworths doesn't allow exchanges without the invoice. I know other stores exchange if u have the tag. Poor service.