what claim do I have against a prospective employer who contacted my present employer who now shuns me ??

As an employee at will your employer is free to discharge individuals such as you "for no cause at all". Nothing you post suggests that discrimination is going on based on gender, age, race or any other protected employment class was the cause in whole or even in part of your situation.

Good luck to you.

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Not much, unless the present employer disparaged you or made false statements about you, which will be quite difficult to prove. If your current employer is harassing you or making the workplace "hostile", you may be able to seek relief from the EEOC or your state's companion agency, if any.