Bad customer service/senseless return policy

I bought a dress on the 28th September 2023 for a wedding. I unfortunately could not wear the dress because of the weather. I returned the dress but the slip was misplaced. I went back to search for the slip and I could not find it. I still could not find the slip. I went to YDE again today (09/10/2023) and YDE refused to refund me my money without the slip even though i could prove the transaction and date on the banking app. they gave me an option to get something else or a gift voucher. I refused both the options and they said they could not help me without the slip. I do not want anything from there as you cannot get any item for day to day wear and i do not have any event to attend. If they can give a gift voucher why can they not give me my money back.