My son was sent 2 a behavior center by a deputy & they wont let me take him out?

Its been almost a full week, my son was taken to a behavior center from a deputy without my consent. And the center is charging me 800$ per day and they wont let me take him out, its been almost a week. They wont me to sign a voluntary admittance paper that in the fine print allows the doctor to keep him if he wants. What can I do, to get him out?