Gift cards not being redeemable (UK)

A couple of gift cards I have purchased have not worked, one was for Wagamama 6 months ago, I eventually got a refund in CRO however this basically put me well out of pocket as took over 2 months to resolve. This week I purchased a Just Eat voucher, it has been issued 3 days ago, but I have tried to redeem the last few days with no success. Error being: * **Voucher or gift card code not found** Has anyone else experienced this or am I just unlucky, CDC are not responding to my support request and I expect it will take another 2 months of chasing to get anywhere....