Can’t delete birthday from a contact I deleted

Check the calendars you are syncing by going to Settings > Calendar > Accounts. If you are syncing from another calendar and it is that calendar that has the birthday, you will need to delete it from that calendar. For example, if you have a gmail account, then you may be syncing that Calendar and will need to delete it from your Google Calendar.

Find out which calendar it is coming from by going to the Calendar app and choose Calendars on the bottom of the screen. Uncheck all calendars and add them one at a time until you see which one displays the Birthday.

Yea, I thought so. You will just need to remove the birthday from your Google Calendar by signing into your Google Account online. You can then sync your Google Calendar again and it will be gone.

If you did not add it to the Google Calendar yourself, then you might have the Gmail app or another Google app that has access to your Calendar information. Check which apps have access to your Calendar information by going to Settings > Privacy & Security > Calendar.