When you take the back battery cover off you can try to use a small screw driver or you finger nail to bend the USB port a little to see if that helps. You can also attach a USB cable to charge and then, while charging, try to bend a little and hold to different degrees to see if that starts charging normally. This is likely what your guy was referring to. It's not a solution, maybe temporary, but it will tell you whether it's the USB charging port if it reacts. If it doesn't react then it can be many other things as well. So while you have the back cover off make sure the battery sits correctly.
If the battery sits tight and snug then it could well be the USB charging port that got disconnected due to damage or dislocation. There is a DIY on how to disassemble and you could try to replace it yourself or resolder (w w w.youtube.com/watch?v=L1kdLtnC9gY&index=2&list=WL. Starting at 3min it shows how to take the board off that contains the USB charging port. You can see that better at 6:30min. You could investigate whether it broke off or is loose or entirely damaged.
Replacement parts on ebay).
However, the first step is to contact the seller or MS to get it fixed since it should be still under warranty.