My inclination would be to ignore it if you are getting on well without them, esp. as far a family/friends. If you really think they could d/f somehow if you don't call them back. Then call them, but do not really SAY anything. ASK them who has slandered you by saying you have "left Jehovah," and that you would like the opportunity to confront the individual in order to deny it.
There---you have now instilled worry if not fear in the elders mind. Now he may have to actually do something "by the book" You have not acutally said you have NOT left Jehovah, but that you could if if a lying slimeball is produced.
Oh, and you are so hurt by the whole matter that you can't bring yourself to even meet with them.