Okay, I contacted the Kilt Store, and got this reply:
Thanks for letting us know Gary! But I'm writing from home (no rest for the widked!) and I probably can't do anything before Monday. But fyi, we'll be happy to honour the discount if you want to make any purchase meanwhile. Just mention the problem at the checkout and our team will discount it accordingly! Feel free to share this info it it helps...

Thanks again and best wishes

Nick
So now everyone knows.