Hey
If you find your stuns are doing nothing in PvP, they probably had a full bar of resolve which would make them imune.
Its a widely used tactic so have a ballcarrier with full resolve do the last run in huttball.
Just check the little curved bar thats on the outside of the enemy portrait, if its full, dont use your stuns.
Also a good trick in pvp is to use leg-slash first before a bigger slow/stun. If they are not very experienced they will pop their escape button, and you can safely use your longer cooldown abilites to keep them still. This trick will not work if you meet an experienced pvp player, but it never hurts to try ;-)