Fraud: Can they hold this stock ransom?

I am an artist. About 3 months ago I received email from interested art buyer. We agreed on $5,000 for an oil painting. The man sent the cashiers check. I did not have a valid Drivers License ID so a friend lets call (John) of mine who has a friend lets call (Joe) who works at a bank cash the check for the cost of $200.00.

I paid off my bills and three weeks with the $4,800 I got back. Later John comes and tells me the check was bad. That I owe Joe at the bank $5,000
He gave me no proof of that the check was bad.

John then went to my boss (who is friend) and told him and got my stock certificate worth $50,000, 2000 shares at 25 dollars a share asking price is not $2,000.

This$ was without my permission. I told him if he gave me my stock (I worked 8 months free for this stock) that I would go to my broker and get him the $5,000. He said no. The banker (Joe) has already charged me $2,000 in interest. (It’s been only 3 months)

First off, when I gave John the $200 to Joe to cash the check I would assume Joe would check to make sure it was a good check. Since he works at the bank.

Second, can they take my stock worth $50,000 and not give it to me?

I have asked John for the proof of the check but he still has not come up with it. I also asked for my stock and he won't give it to me. I would want proof first of the bad check and then if all turned out OK, I would pay him the money, but I don't want to pay these loan shark interest rates he is charging as he holds my stock at ransom.
And I need the stock to use to pay him.

Yes, I know my boss should not have given him the stock, but it’s done and now I just want it back. This bank guy (John) knows I just quit my job and I cannot afford to pay him out of my pocket now, I need that stock to use to pay him.

This guy I feel had no right to take my stock, my stock opens at $25.00 but and asking price is now $2,000 a share. I have 2,000 shares (preferred). How can he hold $50,000 worth of stock for a $5,000 dept (if there even is a dept.)? What do you think I should do? He holding my stock is hurting my finances at the moment.

If the banker Joe wants I told the "go between" (john) that he can go to the broker with me to get his cash. It would seem the banker would just want to be paid for the bad check, but it seems not. WHo knows, maybe they illegally signed my name and cashed in the whole amount. I just don't know since they are not willing to work with me to get paid back.

I am thinking of just going to the District Attorney's office and try to straighten it out there. What do you think?

Thanks,