No refund as it's not there fault.

I purchased wiper blades and other items for the 1st time but returned the wiper blades as it was the wrong size. I used a voucher for my 1st order. When asking for my refund they sent me another voucher. Now when trying to use the voucher it says expired. When asking them how can it be expired they told me there is a date below the voucher. How should I know the date below is expired date. Now they won't refund me at all after telling me it's not there problem.