No exchange even with proof of purchase and all labels in tact

My friend ask me to buy a pair of jeans at the waterfront store for her . Purchased 18th May . My daughter thought they were for me took them out the bag ( which had the receipt in) and it got thrown away. Friend comes gets the jeans brand new with all labels and tags on . Jeans slightly to snug so within 4 days tries to take them to just swop for a bigger size with proof of purchase from my credit card . Goes to canal walk and Waterfront. She cannot even exchange They are offering no solution , no phones get answered just a voice note to say no refunds or exchanges without receipt in fact the consumer act says proof of purchase. Nobody will even talk to her they just say no receipt no exchange . It says proof of purchase ? It was within 7 days she tried to return