WW return policy – the stuff that nobody tells you

Bought underwear at Gezina WW, had to exchange because the fitting room was closed. Exchanged and the fitting rooms were still closed. Specifically asked if I may return it if it didn't fit. Kept EVERY slip that i got. But the one i payed with was kept by WW the previous time I exchanged. So when I asked for a refund they refused to refund the card I paid with because there was no slip to prove that I payed with that card. Well duh! Of course I don't have it because you kept it with the first exchange. So I get issued a voucher, useless. What do you think Edgar's will say when i produce the voucher to pay for something that fits? Please tell me how I am supposed to be okay with this. Now I have to make peace with NOT being able to purchase the items I need from another store, because the money I need to make the purchase is stuck on a voucher for WW, so the items that I need, I have to do without because I can't take the voucher somewhere else. And all of this because I returned the product with the slips that YOU, WW, handed me. How is that okay? To take away my right to choose where I spend my money. I have always praised WW for service and products, but this for me is completely unacceptable.