Hi, my korg X5D have malfunctioned pitch bend and modulation wheels. They dont respond in any way, not even when i try to calibrate them.... What should i do ? Also, this is absurd question maybe, but on the downside of my X5D, little sticker says model : X5, and when i start the keybord, in the welcome message also says X5. But the whole case (plastic) is X5D case. Is there a chance that seller tricked me or this is standard on all X5D ??

The pitch and modulation wheels are on a separate circuit board, if they both stopped working at the same time, it's likely the connecting cable has dislodged.
Opening an X5(D) is relatively simple and you should be able to simply plug the cable back in. If you're not comfortable doing that, take it to a shop.

You can't always believe the display in regard to the model... Try finding the revision level display that will tell you what you have... It is NOT likely a seller would strip a X5D case to try to fool you.
Find what the difference is in the model and test your unit for that feature.