Rear parking sensors malfunction

My rear parking sensors are not beeping. Initially when I select reverse, there is a single beep and then silence from them(other than the standard reverse beeper from the car).

I have tried switching the button at the trunk to both positions, no difference. I can also "feel" the vibration-pulse of each sensor when I touch them. This probably means that they have power but somehow the signal is lost between the rear of the car and the (front?) beeper. Front sensors beeper is at the front, I don't know where the rear is or if it's the same. I'm wondering this because I've read some other thread here that has a PDF installation guide on the Gen3 Prius and it has a rear beeper from what I understand.

Any help for the location of the sensors hub or other locations I should check for disconnected cables will be appreciated. Bonus question for someone who may know is how can I permanently disable the front sensors because they are redundant and I can see at the front .

European Gen 2 Prius 2007 model without the reversing camera.