Doorbell camera not working

I have the Xfinity Doorbell, the first one worked for 10 minutes until I activated voice/sound, then it died instantly, I received a 2nd Xfinity doorbell and it worked fine for just under 2 wks. I contacted techs, again trouble shooting, I had a 16vV transformer 

A 3rd doorbell had been sent out, before installing I upgraded to a 24V transformer, camera worked fine, live worked fine, until I used the doorbell then the camera is dead again? I am at a complete loss as to the problem?