Sally:
It isn't worth it. Any satisfaction you may feel will be short lived.
I've been in the position that I have known things about people which could cause major problems in their lives and have been faced with them doing some very nasty and hateful things to me, yet I didn't retaliate by opening my mouth- even when they came back for another round of their version of nasty treatment. I figure the way they have acted shows their own lack of integrity and decency and I still have mine intact. Let them live with that fact and laugh like little school children amongst themselves about how much fun it is to treat another human being in such an awful way. But then- I won't feel any angst for them when they lament about how awful they've had it in their lives because they didn't learn a damn thing from it. They are basically continuing on in their lives to treat others in the same way they complain they have been treated themselves.
Take the high road. It can be very frustrating and very tempting to respond in kind- believe me- I still feel that way now. But in the long run you'll be the better person and they'll still be little school children flailing about in their miserable and shallow existences and you will have shown to yourself that you can rise above it and leave it behind you. The way they have acted is not kindness by any stretch of the imagination and karma is a very interesting thing. And if others choose to believe what they are saying without knowing you- it says something about them as well.
Hold onto your integrity and your honor- don't give it away just because others have proven they don't have any.
my 145 cents
XW