I don't think you can just walk away, and simply stop paying. Check your contract and see what formal notice period was required when you didn't want to continue. Just because you see it as a fee doesn't mean it is optional legally speaking - they have to continue with the maintenance and they levy a charge against the points people have bought, whether they use them or not. As I see it you have points that they are abliged to honour, should you want a holiday and they can't allocate them to someone else without your say so.
You might not be able to sell them to someone else, but there must be a way for the company to take them back or just cancel the agreement you have. But you need to have informed them.

Jan