iPhone not showing contact birthday notifications

I want my iPhone to show notifications when it is a contact's birthday. I have set contact birthdays in the Contacts app. I can then see these birthdays correctly in the Calendar app. I want to get ONLY birthday notifications, not other Calendar events. My settings are set to the following:

Within Calendar apps

• All calendars unchecked except for Birthdays

Settings > Apps > Calendar

• Default Alert Times: Birthdays, On day of event (9AM)

Settings > Notifications > Calendar

• Allow Notifications: On

• Alerts: All styles checked

• Banner style: Persistent

• Customize notifications: All unchecked (As no birthday option is available)

Any help would be appreciated, thanks!