Relocated and can't return to the old job.

I was relocated to a foreign country three years ago by my old boss. Although he didn't give me a written promise to hire me back, he did tell me verbally that I could come back after a few years after some of the senior members of the company retires. I also have a letter stating that I "could come back if fund is available". Now, my boss is telling me he won't be taking me back. I have never been given a notice of termination by anyone before this. He said that his decision was based on my "prior performance". However, I have never been told by anyone in the company that my performance was sub par. I don't even know if there exists a systemic evaluation process. As a result, I am left in a foreign country with a difficult prospect of coming home to a new job. I feel I was unfairly dismissed. I have also found out since coming to this foreign country that I have been told a lot of lies just to commit me to come here. My boss also threatened to not renew my contract before offering me to relocate me.

Do I have a case against my old boss/company? Thanks for help.