Tl;dr Can A Company Force You To Sign A Second Contract And Keep Your Money If You Disagree, If You Signed One First Non-refundable Contract?

I'm a small artist and vendor, I follow all my tax laws and all my required registration laws. I signed up for an extremely small event across a state border, one I was anticipating losing time and a little bit of cash at anyways (bad fit, but my mom really wanted to go and I was going to treat her for mothers day.) I knew the event was Non-Refundable, and when I spoke via email with the event planner, was told that theres no big rules at all, just that I was required to follow all tax law, parking was at the discretion of the hotel, and that I would get an 8x8 booth and one helper in there for the price of my registration, bring my own tables and setup materials. Nothing else important. Perfect, fine, I dont care.

One week before the event, ie, today, they sent me an email with an additional 4-page contract, listing all sorts of rules that are required for their event, inclusive of being 100% required with no exceptions to submit paperwork that is not necessary or relevant to my business. They told me that the signature and adherence to this contract was absolutely required if I wished to sell there next week, and if it wasn't, I wouldnt be allowed in.

Now, understand. I sell tacky souvineers with my original characters on them. Keychains and googly-eyed plastic clams and grabage like that. This was going to an event for "holistic healing" and shiny rocks. I dont understand why they needed to recieve my "sharps certification" (which I dont have and dont need, I dont work with medical needles or any kind of other sharp) or over 15 different certs from the copyright and trademarking office, one for every one of my own characters. The expected turnout for this is the equivalent to a christian church bake sale. I think they are making a much bigger to-do of their event than they actually need to.

I told them that this is NOT part of our original contract, and that I absolutely would not sign it- Nor can they keep my money if they insist that I have to sign it. I told them "You should probably have this available and in bold on your website."

A completely different company- who informed me via email that they had nothing to do with the original company and had "just sent out the flyers as a favor" said "Youre wrong- we dont NEED to do that. we NEED to have a refund policy- and its NO REFUNDS. Understand what we're returning your money despite us and all our affiliates being a non-refundable event, but its not at all our fault that you sent us your cash before we sent you our contract." and have banned me from all of their future events. Banning me is no big deal, i sincerely dont care and my mother hates me anyways- But their carelessness and horrible reading comprehension has rubbed me just the wrong way enough.

Is keeping my money and refusing a paid-for sublet service over refusing to sign a secondary, secret contract a thing they can actually do?