A school district interviewed me on and off for 5 months before offering me a newly created position. I gave a 30 notice to my employer. Three weeks later the school district rescinded the offer claiming an unsolicited phone call gave them information which would preclude my employment. I was now training my replacement and could not get my former job back. The school district refused to tell me who called or what was said.

Since there is nothing in my background to warrant this action I suspected the school district of age discrimination and filed a grievance against the school.

I have since heard through " the grapevine " that the caller was a staffer of my former employer, and that the caller told the school I was going to get another bad work evaluation. All of these claims are untrue but the school district chose to give this false claim more weight than my references and take the offer off the table.
Any thoughts on possible actions on my part ?