Help - Issues with my Parking sensors

Hi everyone,

I am at my witts end with my parking sensors on my car and I am hoping you guys maybe able to help shed some light on my frustration.

I have a 2013 Mercedes c220 CDI (W204)

Right bit of a background, I bought my car from a Garage about 3 months ago and everything was working fine as I left the garage. Pretty much as soon as I got home the parking sensors stopped working.... Having had faulty sensors before it didn't really bother me too much to replace one.

I did the whole "click" test and listened and found the faulty sensor.

Upon removing the front bumper it appears that the car has had a front impact at some point in its life. I ended up changing what i believed to be the faulty sensor and put everything back together and this didn't fix the problem.

I took it to a local garage and they diagnosed 3 faulty sensors. So I decided to instead of risking another failure I would replace all of the front ones. I replaced the bumper and once again no joy.

I now don't hear a "clicking" from any of the front sensors (which I get from rear sensors) I've checked all of the fuses and also sprayed contact cleaner on all of the connections.

I quite literally have completely run out of solutions to fix this very annoying problem. Any help or advise would be really really gratefully appreciated.