I found this out too. [exists] works off target afaik, don't think it'll work (try it out and let me know). I changed to something like this:

/cleartarget
/targetexact ziggy
/targetexact jiggy
/targetexact biggy
/focus [exists]
/cleartarget

It will remove your current target (you can use /targetlastenemy or /targetlasttarget at end if you want), probably some ways to improve it but it works for me I had just switched to Jamba too so I was beating my head trying to figure out what was going on, lol!