Good luck with pallies at the same gear level as you. Hammer of justice and bubble, combined with the plate armor, make them very hard to kill without a few lucky crits. With shammies, you can kill them if you keep them from healing. You have quite a few ways to do this: Pounce, Maim, Cyclone, Bash, Feral Charge (bear), War stomp (this is assuming you are tauren, ignore if not), restealth > pounce after a maim or cyclone. Generally, I go with something like Pounce, Mangle, shred, tiger's fury, shred, maim to interrupt heal, shred until maim is about to break, bear form, run away a bit before they start the heal so I can charge it, mangle, bash the next heal, mangle, cyclone, cat form, maim, etc. That is actually more than enough to kill one. Watch out for them trying to break los if you break contact to bear charge them. All you have to do is remember you have more than one trick up your sleeve, more than one form to use, more than one way to keep them incapacitated.
I would suggest getting a guildy healer to duel you a few times so you can get the hang of using all your interrupts. Tell them to just spam a quick heal, not actually trying to win, until you are pretty good at interrupts, then do it a few more times with them trying. Hope this helps.