If your Samsung phone is going straight to voicemail without ringing, here are a few things you can try to fix the issue:
1. Check your phone's volume settings: Make sure that your phone is not set to vibrate or silent mode. Ensure that the volume is turned up and not set to low.
2. Check for Do Not Disturb mode: If your phone is in Do Not Disturb mode, it will not ring. Go to Settings > Sounds and Vibration > Do Not Disturb to check the settings.
3. Check for call forwarding: If you have set up call forwarding, the calls will automatically go to voicemail. To check the call forwarding settings, go to Settings > Phone > Call forwarding.
4. Reset network settings: Resetting your network settings can help fix this issue. Go to Settings > General management > Reset > Reset network settings.
5. Update your phone's software: Make sure your phone is running on the latest software update. Go to Settings > Software update > Download and install.
If none of the above steps work, then contact Samsung's customer support for further assistance.