My calls are going straight to voicemail

You may have Do Not Disturb enabled.

When you have a Do Not Disturb turned on, a crescent moon icon  appears in the status bar and on your Lock Screen.

Follow these steps to Disable:

1. Open Control Center on your iPhone or iPod touch, or on your iPad (see image below)
2. Tap Focus, if any of these are listed as On, click it to turn it OFF. 

For more information about Do Not Disturb:

-> Use Do Not Disturb on your iPhone, iPad, and iPod touch - Apple Support