my phone stopped ringing on my iMac. Why?

On the iPhone, check Settings > Phone > Calls on Other Devices

• "Allow Calls on Other Devices" = "On"
• "Allow Calls On" contains the Mac in question

On the Mac, in FaceTime, check FaceTime > Preferences > Settings > Calls from iPhone = "On"

And, of course, the iPhone and Mac must be on the same Wi-Fi network.

Glad it's all working now.

Yes, there are additional changes required once an Apple ID or its password are changed.

Enjoy your Apple gear.