Did you have it in writing that you were supposed to get the G50 series? This is there Elite series and is a step up from the G40 Merit series. The warranties on the two are the same. The Elite series will be a little less noisy as it is better insulated and is an upgraded model.
If you hae it in writing you were supposed to get the G50 I would push the point to get it or ask for a credit on the difference in price.