I own a echo 1 vector arms mp5a4 ras, but the stock orange tip won't come off... what do I do now?!?

I can't lift the orange tab thing, push it down, i cant push it forward, nothing. I've tried to just twist it off cw and ccw. Still no luck. is mine a lemon or something? I really need help before i break it. Its already pretty torn up. And its aggrivating. If anyone knows what to do, please say so or give me a link. links to instructions would really really help. Thanks!