Both front and rear sensors work similarly, but they have a slightly different pitch so you can tell which ones are sounding (it’s possible to have both sounding simultaneously in a tight space). If they are working correctly, then as you approach an obstacle you get an intermittent beep, which becomes more frequent as you get closer, followed by a steady tone when you’re very close. The distances vary front/back, the handbook tells you what they are. At the same time both the centre infotainment unit and the right-hand multi-info display will light up to warn you where the obstacle is.
As you’ve checked that everything’s turned on, then it looks like you have a fault. Depending on exactly when your car was first registered it may still be inside the 3-year warranty, if so I’d get a dealer to look at it.
Edit: above comments are from my experience with an SE, which doesn’t have the reversing camera. I assume it’s the same with your EX, but I’m not sure how the camera works with the rear sensors (front sensors should work the same on both cars).
