The general rule is that when someone is hired as either an employee or a contractor, and is paid for work, the work they do is considered "work-for-hire" and is the property of the employer, regardless of whether there is a contract or not (although a contract can stipulate something different if the parties decide to do so).
However, if the employer did not pay or made any representations that the product created would be your property, then you may be able to file a civil suit against them for either additional money or ownership - but that is something only an attorney who fully questions you about the facts involved and reviews all circumstances of the case can tell you.
Also, if the "false information" you say they are saying about you is preventing you from being rehired or otherwise damaging your reputation, you may be able to file a civil suit for defamation against them. A defamation suit normally requires that a party state or print, to others, lies, that harm the reputation or character of a person. Again, you will need to speak to an attorney about all facts invovled.
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