You may have cliams for libel and/or slander, and also for tortious interference with contract, but would have to know more about the facts of your case in order to be able to give you any opinion about the strength of your case or its potential value. I suggest you make an appointment to speak with an attorney and get some advice.
Employers do have a certain amount of immunity to provide references upon request. However, you may have claim if they acted outside of the scope of merely providing a requested reference.
More information is needed to determine if you may have a claim. However, please remember these type claims are difficult to win because of 1st Amendment issues. Nevertheless, based upon the information you provided, if they are purposefully stalking you by calling and providing unsolicited information to your employer, you should have several causes of action.
I have handled defamation matters. So, if you need additional information, please contact me for an appointment.
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