Good morning Camelotshadowjade! I am sorry this is happening! I hope I can offer some insight, but this is only from my knowledge and not rule of law
Nephrite is inert under UV light, and shouldn't glow at all. It's notoriously difficult to dye, bleach, or impregnate due to its structure of tightly interlocking stone fibers (which is also the reason its tougher than jadeite). So as a result, nephrite is usually substituted rather than treated. My guess is that your piece might not be nephrite, but a treated agate, onyx, or a type of quartz. Stone treatment and substitution has been perfected over the years and can look pretty close to the real thing whether it has a certificate or not.
I know this is easier said than done, but try not to feel bad. This is all a part of the crazy maze of buying nephrite/jadeite. I'd say get in touch with the seller as soon as possible and return for a refund - but I wouldn't fuss with him/her about them knowing whether or not it's real. Speaking generally, most people selling stone jewelry these days are 3rd party sellers who have very little intimate knowledge of the pieces they're selling. Just try to find reputable sellers you can trust - that will remove some of the hair-pulling of this experience.
Trust me - I feel your pain. It's hard when you spend hard-earned money (and emotional investment) for an item and it isn't what it should be - but it does get better