Can my parents remove my door/lock as an adult?

For context, I live in Wales with my parents as my landlords. I am disabled and autistic, and have had to call the police on them more than once for how they treat me. I have tried escaping them multiple times but have no way of saving money as I'm currently too sick to work (I do have a team of specialists trying to help get me well enough to do so, but it'll take a while) and UC won't help with rental payments if they're to family.

They just threatened with removing my lock and potentially my door from my room if I keep "disrespecting" them by having meltdowns/shutdowns when I'm overstimulated or overwhelmed. They know the only thing that helps me calm down in that situation is separating myself from people somewhere I can ensure I'm alone, hence why they're saying they're gonna make sure I can't do that.

I don't have a formal rental agreement, but I pay ⅓ of what's in my bank every month into the household and whatever is left at the end of the month too.

Do they have the legal right to do so, given we don't have a formal rental agreement? If so, are there any steps I can take to try and get an agreement where they can't do this to me? I'm scared of what will happen if they have 24/7 access to me.