How to stop an app from running completely on OS X?
It is probably a launchctl process that is restarting.

To see all loaded launch agents, in Terminal: 

launchctl list


To remove one:

sudo launchctl remove label_of_program_to_remove


where, label_of_program_to_remove is found in the preceding list.  Note that you have to run the sudo command from an administrator account; or, su to an administrator account first.