Dealing with someone (mom) who won't take "no" for an answer?

That was my thought too. Has she actually threatened you, or are you afraid she will if you stand up to her?

Either way, get replacements of your important documents, a safety deposit box, and don’t tell her where the key is.

You may want to look into some self-help books on setting boundaries, or seek advice from a therapist. Bottom line, you are an adult. You are allowed to say no and not be sent to your room without supper.

Just out of curiosity, why do you fully anticipate that? Has she used the documents as leverage in the past? Or alluded to it as a possible means of asserting her dominance over you?

ISTR that some time ago you mentioned BOTH parents reacting badly to a relationship you were pursuing. Did I get that wrong, or is your dad still in the picture, and if so is he still living with mom, can he be enlisted to lobby on your behalf?

Next, have you spoken of this issue with your friend? Your friend might be only too happy to have you share the number with your mother (and possibly willing to call her and lay down some ground rules about what boundary expectations your mom would be subjected to, with number blocking being an available consequence for their violation).

If your friend is unwilling to let you share the number, subterfuge may be called for. You could have your friend call mom from a different buddy’s cellphone, and the caller ID could be converted into the contact for that friend.

I don’t know how to handle the immediate crisis of your mother extorting you for your paperwork, but I would get my hands on those papers no matter what. Maybe consider giving her fake contact information in exchange and then I would leave skid marks in her driveway getting as far away from her as possible.

I would use the big move as an opportunity to put a moratorium on contact with your mother and then when I did resume contact, I would do so with some boundaries. It is easier to do that with the distance, you can always end the call and turn off your phone.

Are there any redeeming qualities that you find in your relationship with your mother? I gotta ask because you make her sound like an awful shrew, yet you are seeking help in navigating the relationship.
I am in my 50s, and have lost both of my parents. They weren’t controlling as you described. But they weren’t perfect either.
I see a lot of comments here suggesting you cut ties with your mother. Will you be comfortable doing that?
It’s your life, remember. Don’t lose your mom (if you don’t want to) based upon a stranger on a message board’s advice.
PS I wouldn’t give out the phone number but I’d probably tell her that I will be in touch during the week and don’t worry about me.

In my case, I had the advantage of precedent to help me through awkward situations like these with my (recently deceased) mother.

Mom: But you don’t let us know what you are doing or where you are!
Me: Like the time you and Dad went to Romania for three months without telling me you were going? And I didn’t know until you were there two months and my brother happened to mention it to me?

Mom: I’m so saddened that you and your siblings don’t visit more often!
Me: Like when you and Dad moved the family across the country when I was eight and we didn’t see our grandparents for over three years?

I just wanted to link to the excellent guide to drawing boundaries in today’s Washington Post. (I believe you can get a number of free articles every month by creating an account).

The whole piece is worth a read and provides some good examples of how to respond.