That certainly hasn't been easy for you ― let’s check this out.
What kind of Chromecasts do you have and what are the status of the LED lights on the device? What is the exact message on the tv screen? Since the router has been changed, that means the old WiFi is not available anymore. Doing the factory reset is a must. After the reset, reboot your router, Chromecast, then TV. restarting your phone might also help. Before the setup make sure mobile/cellular data is turned off and bluetooth is on. If you're an iOS user, go to its settings>privacy>local network access>disable then enable it.
Keep me posted.