That’s not great, but the contract should be legally binding, especially if they have paid some (IANAL). But Is there some way to turn this into an opportunity? Does the CEO perceive that you are not providing value? Could they describe how you might? It hard for startups since you don’t have any legal firepower.
I would show up in person & try to meet live if I were you. Even if the CEO doesn’t meet with you, you get the ‘upper hand’ just by having made an effort.
Unfortunately if there is a term for convenience clause, there isn’t much recourse. If this doesn’t work, I’d find a competitor, offer a great deal & publish a press release announcing the partnership. We’ve done something similar in the past, and you would be surprised how quickly FOMO leads to deals closed.