Rear view camera

Hello everyone.! Can anybody help me with this? I have the Octavia mk3 A7 5e 2013 November 1.6 diesel dsg . I have bought a rear view camera for the trunk and installed . The wires for camera signal and power all go Infront .I have seen a video about a blue interface and 2 wires I had to put in. I did all that but still no picture . After that I bought a cheap 4 inch monitor to test . It shows the picture perfect. I think that the camera has power but for some reason the signal does not go through the CD module. Can anyone help me? It's driving me insane. Adding to the above I've been to my mechanic and he has activated the rear view camera feature through vcds . The result is that when I put my car in reverse I see a black screen and some adjusting I can do with color etc. And a warning down. But no image. I have enabled the driver assist as well but nothing. PLEASE HELP.