And you have not ever removed the camera in those 3 weeks? I ask because when removing/replacing the camera, one of those spring contacts between the camera and the bird can be caught pushed down... so it does not properly make contact. But you can easily yet carefully, pull that spring free with a toothpick or a small screwdriver.
If not, it is possible to do a factory reset to the controller and subsequently repeat the new model, rebind and reconnect to the ST-16 to see if the gimbal will react to controls. As far as flying, your limitation will only be in terms of being pilot's view only... as long as the camera is indeed facing forward.
If none of this works you may be making a call to Yuneec CS on Monday. Make it early... they open at 8AM PT.