This game does weird things from time to time. I have completed a couple things that i never got rewarded for either. Quick question though...Did you level up ANY part of this weapon while in combat training?
If the answer is yes, then none of it counts towards your calling cards or challenges. It only levels up the weapon and your regular level. NOTHING ELSE.
If the answer is no...then you will just have to keep playing and it will probably just give it you eventually.