So you were trading your gems to the Huns, the trade ended (returning the gems to you) and you say you have no luxuries to trade? If the Huns acquired their own gems, they certainly will not trade for additional gems (additional copies offer no value).
Go to the top left menu (which normally shows what tech you are researching) and select the resources tab. That will show you how many instances of each luxury, strategic and bonus resource you have. Does it show 2 gems? If so, have you tried trading gems with each other AI civ? If no one wants gems, it's because they already have gems from another source.