RTU, is Right To Use. Not deeded. There is nothing to foreclose. The only hold they have on you (assuming it's paid off, and all you owe is annual fees) is the ability to use it. Write them, tell them you're done and are not paying them any more and they are welcome to use the contract for toilet paper. You won't be back. How's that for easy? Highly unlikely they'll ding your credit, and if they do, you're welcome to write a rebuttal with the credit agency. I can't imagine anyone who checks your credit holding a default of a Mexican vacation club against you. It might even improve your credit because you'd have less debt.
Jim