Highly Embarresed - Could not redeem voucher at Tyler's Umdloti

Wanting to enjoy a Birthday Celebration at Tylers's by using a Dineplan Voucher, we were extremely disappointed that when it came time to paying the Bill, we were told that Tyler's (which is listed as a Dineplan partner) , do not redeem vouchers. What made this experience Bittersweet was that we had checked not once, but 3 times prior to the booking that we could use the Voucher. Just poor explanation all round both from Dineplan and Tylers.