It’s not clear from your questions what you are trying to achieve but I suspect that most of them are just common sense, the first part of support is actually helping yourself.
If you want to check the new camera on the old mount then just unclip the old camera from the mount, unclip the new mount from the new camera (this is in the instructions so not rocket science) then clip the new camera to the old mount and plug it in.
Then to test the new mount on the old camera just clip it on, power up and see if you get FPS signal.
These are all very basic, obvious and simple tests to determine where the fault lies.
Realistically, if you initially put the camera/mount in the wrong place, then had to remove the mount and reposition it on your window, chances are it was damaged at that point and the fault has now developed.
Also in relation to support, you need to take into account time differences.