Want to return a gift? Dream on....

Have just tried to swop/return/change to giftcard 2 tops tgat were give as gifts for Christmas to my children. Cavendish H&M refuse to help as i do not have a reciept. WHY WOULD I HAVE A RECIEPT IF THEY WERE GIFTS!!!! I cannot ask giver for reciept as I would seriously offend them and to be honest they probably threw reciept out as gift was given. What do i do? Management was extremely unhelpful and uninterested if finding a solution.