Character Defamation on Work

What case can i file and do i have the rights to file a case?

Heres what happened:

im a married man with two kids..recently someone messages my wife in her phone saying that i am the father of my co-worker's 2nd child..and that same number also texted my manager and keeps on saying the same thing..the unknown texters keeps on saying that me and my co-worker is in an intimate relationship from 2009 til now..i admit that i had a relationship with my co-worker but it ended last August 2009 and then i got married December 2009..i can prove that its not my child and my co-worker is willing to help me..
we where about to find out whose texting me, my wife and my managers..now it was a "tsismis" in my workplace..and it really cause psychological damage to my wife and my co-worker..my wife wasn't able to go to work for 4days because of those messages..she missed all her daily incentives and bonus, and been absent for 5 days..

im happy to tell you that we where about to find out whose that unknown texter..

what should i do if i found out who started those "tsismis" and that unknown texters? what case can i file against him/her?

thanks..i hope you could help me with my situation..

You can file a case for unjust vexation

i dont think its just unjust vexation..because the texter is already causing psychological damage to my wife..

finding out who is behind this is more of an investigative problem, not a legal one. i would say that the case to be filed should be libel.