Holiday Extras Duplicated Trip - Full Refund Due, Voucher Unused

I’m trying to get a refund from Holiday Extras for a trip that was duplicated. I was given a voucher, but when I tried to book a new trip, there was no option to use it, and I was charged the full amount again. After reading the terms, I realized that since my booking was made within 14 days, I’m entitled to a full refund instead of a voucher. As I’m unable to use the voucher, I would like a full refund of £26.11.