Misleading Advertising

I was gifted a gift card to purchase an Air fryer about 6 months ago. I searched and found one and was ready to pay. Only I could not buy it in the shop. I tried online and again I found it but can't use my gift card to pay for it. Today at the shop I am told I can't use the card online as marketplace is a different platform to the store! But nowhere we are told we can't gift card to by online . Now I am stuck with a gift card I can't use as all I want is an airfyer. How misleading is this? I spoke to Debbie Powell who claimed to have spoken to others and insisted I can't use the card. Now what?