My reading of Discoveread's analysis of the governing law and the process is that they are probably correct. The UK falls into "any other jurisdiction" under the contract, and the T&C are clearly state that:
If you are a User located in any other jurisdiction, you are contracting with Eventbrite, Inc., a Delaware corporation, with its principal place of business at 535 Mission Street, 8th Floor, San Francisco, CA 94105, Reg. No. 4742147 ("Eventbrite US").
There's also a clear warning to be aware of the binding Arbitration clause in the case of disputes, such that any disputes can only be settled by arbitration (to take place in SF) or a small claim. Starting the small claim in the UK is highly likely to be opposed by Eventbrite on the basis of non jurisdiction, as you usually need to start a claim in country whose laws govern the contract. The contract stupulates:
These Terms are governed by the laws of the State of California, without regard to its conflict of laws rules. These laws will apply no matter where in the world you live. But if you live outside of the United States, you may be entitled to the protection of the mandatory consumer protection provisions of your local consumer protection law. Eventbrite is based in San Francisco, California, and any legal action against Eventbrite related to our Services and that is not precluded by the arbitration provisions in these Terms must be filed and take place in San Francisco. Thus, for any actions not subject to arbitration, you and Eventbrite agree to submit to the personal jurisdiction of the federal or state courts (as applicable) located in San Francisco County, California.
I think it might be too late to opt out of the Arbitration, that's how I read it just skimming through the terms.
That doesn't mean any claim is dead in the water. There might be grounds to apply for any claim/any arbitration to be heard in the UK, as your initial contact was made through the UK part of their business, and it may well have been a UK based operator who pulled the plug on you. And they will still need to justify pulling your event under the discretionary terms of the contract, which as I mentioned above, may have been exercised without any rational basis. And yes, your lawyers need to check how UK CPA and EqA laws may come into play.
My DH does a lot of this type of work for clients engaging in cross jurisdictional legal agreements, I will ask him tonight what he thinks.