Horrible experience with Brits MrP

I purchased clothes and used my bank card to pay (standard card not credit card) 2 items where not of the correct size and returned it and was told i can't be refunded because i didn't have my card with me okay.... they issued a voucher which i have been trying to purchase online and pay it says Voucher invalid. So now i don't have my money nor can i use the useless voucher i received