Hi dshuler2020,
Thanks for your post. It sounds like your calls are going straight to voicemail on your iPhone XS Max. We've got some helpful things to share for this.
- Do you happen to have a Bedtime routine set up? If so, does this happen during the scheduled Bedtime? Check in Settings > Do Not Disturb and Clock > Bedtime > Options in Upper Left Corner - Do Not Disturb During Bedtime. If currently enabled, disable it to test it out.
- Do you use a MVNO carrier, such as, Boost, Virgin Mobile, Cricket, etc.? If so, try disabling VoLTE in Settings > Cellular > Cellular Data Options to test.
- In Settings > Phone, do you have Silence Unknown Callers enabled? Try to disable this option and test.
- Does this happen with specific contacts? Could the contact be blocked? To check go to Settings > Phone > Blocked.
- Could you be using a call filtering app? If so, disable the features within the app, remove the app, restart the device, then test it out.
- Try to disable VOLTE in Settings > Cellular > Cellular Data Options > Voice & Data.
If you tried all the steps above, you have good cellular signal, this could be related to a carrier block. You may need to contact your wireless carrier to ensure there is no blocks for spam or unwanted calls.
Should it persist, then we'd recommend to Contact Apple Support
Hoping this helps out, take care!