It’s on your title, what they have done is irrelevant, you weren’t a party to that, and from what you have said it was an informal arrangement. They would find it very difficult to change what is your property right without your consent, I think it would be almost impossible.
I suggest you talk to like-minded owners and consult a lawyer, you need to assert your rights in pretty strong terms. The car space is on your title so therefore it belongs to you.