Very poor service

Help please I went yesterday 19 January 2021 at 4h30 to buy a dress, the dress did not leave the store and before 24hours I asked to refund me my money today 20 January 8h00 as because my wedding has been cancelled, they don't want to give my money back they said they have to speak to the head office and wil take 7 working days. I went in 20 January 15h30 to ask politely to refund me. Also they did not tell me that it's a sale purchase. Due to law I'm aloud to get my money back immediately. Help