How to get in touch with my Santa?

To be clear, I need to message the person gifting to me.

My gift for the space exchange got here today, and it was NOT what my Santa ordered. The invoice is for one of the NASA Visions Of The Future posters, and what showed up was...three panoramic photos of 19th-century Washington DC?

This is absolutely not my Santa's fault, they put in the order correctly and the invoice was correct, but got packed with the wrong order. How do I get in contact with them to let them know? I can't find anything on the site that gives me the option to message them.