I was involved in an accident in April where I was t boned on the rear left wheel whilst exiting a roundabout, it went off for its repairs and since having it returned it’s rear sensors no longer work and it doesn’t even beep when I put it into reverse, there is also a wire that hangs down from the rear bumper but it just looks like it wasn’t hidden properly, any ideas on what it could be so I can try to rectify it myself as I don’t really want to mess around with calling up my insurance just over a sensor. 

I would do directly back to the repairer. I don't see why you would need to get the insurer involved unless the repairer won't put it right.

8 minutes ago, agraham said:

I would do directly back to the repairer. I don't see why you would need to get the insurer involved unless the repairer won't put it right.

Agreed 100%.

The repairer has been paid by the insurer to put the vehicle back to pre accident condition

Probably just main connector not plugged back together.

There is a module either inside the rear bumper on the off side corner or possibly slightly higher beneath the light cluster in the same area if I remember correctly called the PAM (park assist module), possibly damaged or not connected, check that.