As your query relates to a National Trust gift card that was purchased instore, please contact The National Trust customer service team directly.
You can visit their FAQ's on https://www.nationaltrust.org.uk/services/help-centre/gift-cards
Alternatively, you can check your gift card balance by clicking here www.showmybalance.com
If you're unable to find the answer to your query in the online customer service tool, please call the National Trust Supporter Services Centre on 0344 800 1895 or email enquiries@nationaltrust.org.uk