iphone X does not ring when call comes in

1. Go to Settings -> Sound and check the Ringtone and Volume options.

2. Physically check if the Silent switch button is activated.

3. Try to increase the volume of your iPhone to the highest level and then call your number using the other device.

also, check if your call forwarding is on, if it is turn it of. Also, download to the latest ios. If nothing works backup your device and erase all settings and restore it to factory default. Then set it up as a new phone and not from a backup. It should solve your problem. Good luck!

Do they go to voicemail?

Call your network operator and ask (or google) how to lengthen the time before it goes to voicemail