Blocking a contact means your mobile restricts them from calling, texting, and Facetime you.
What happens after blocking?
If somebody calls you after you have blocked them, the calls are redirected to voicemail and they are stored as voicemails on your Phone.
Voicemail Services
You won't receive any notification or any information regarding that voicemail after some time the voicemail gets deleted by itself. This is done so that the other contact doesn't notice that you have blocked them.
Unblocking a saved contact
Unblocking a number is as easy as blocking them, one method is to unblock a saved number and the other is to unblock a contact in recent calls.
Open the contacts
To unblock a saved contact, go to the phone app, click on the contacts section and navigate to the blocked contact.
Unblock this caller
Tap on the name to see the details, scroll down to see the "Unblock this Caller" option and click on it to unblock the contact.
Unblocking a recent contact
to unblock an unsaved number, these are mostly spam calls. Go to the Phone app and navigate to the recent calls tab.
Remove it from the blocked list
Scroll down and find the number, click on the info button to see the details. Tap on the "Unblock this caller" to undo the blocking.