Ex co-worker agreed to be your reference, but disappear while contacted.

I asked my ex manager and another co-worker to be my reference. They both agreed. But, when my potential employer tried to contact them, they disappeared into thin air. It marked an even more devastating negative effect then giving negative comments. I tried to call them, email them, no responses. They are apparently still in the office because their email still work. I asked other co-worker, they didn't take a vacation.

I didn't have any problems with these two co-workers before. I just can't figure out what happened. I am still at shock. How can someone do things like this? My potential company almost extend the offer to me. Then their disappearances caused them to withdraw the offer from me. The only thing I can think is there is a few crazy and super jealousy type old women who like to spread untrue and harmful rumors around about other co-workers. But, I have already left.

I will not use them as a reference anymore. But, what if other co-workers also act like that. Is it illegal for them to do that?