GNK 3+ code doesn't work

[farmergiles]

The GNK code for the kebab main on 3+ isn't working.

It expires on 18th August, but when you enter the code in on ordering, it claims it's not valid. 

[Bluecookie]

Exactly the same for the whsmith code - posted on another thread. I've tried resolving it through Live chat, through email with whsmith. No luck at all.