(a) Initial Ownership.—Copyright in a work protected under this title vests initially in the author or authors of the work. The authors of a joint work are coowners of copyright in the work.
(b) Works Made for Hire.—In the case of a work made for hire, the em- ployer or other person for whom the work was prepared is considered the author for purposes of this title, and, unless the parties have expressly agreed otherwise in a written instrument signed by them, owns all of the rights comprised in the copyright.
(d) Transfer of Ownership.— (1) The ownership of a copyright may be transferred in whole or in part by
any means of conveyance or by operation of law, and may be bequeathed by will or pass as personal property by the applicable laws of intestate succession.
WORK FOR HIRE
Section 101 of the copyright law defines a “work made for hire” as 1 a work prepared by an employee within the scope of his or her employment
2 a work specially ordered or commissioned for use as a contribution to a collective work, as a part of a motion picture or other audiovisual work, as a translation, as a supplementary work, as a compilation, as an instruc- tional text, as a test, as answer material for a test, or as an atlas, if the parties expressly agree in a written instrument signed by them that the work shall be considered a work made for hire
TRANSFER OF COPYRIGHT
§ 204. Execution of transfers of copyright ownership
(a) A transfer of copyright ownership, other than by operation of law, is not valid unless an instrument of conveyance, or a note or memorandum of the transfer, is in writing and signed by the owner of the rights conveyed or such owner's duly authorized agent.
1. If you don`t have a contract (in which they pay you - like in $) you own the copyright
2. If you haven`t signed a release (on paper signed by you and them) you own the copyright
3. If you want to be mean, you could sue them for copyright infringement (and you would probably win)
4. Those are extracts from the copyright law so you won`t have any problems showing this to them.