How to unblock a phone number on an Android phone is described in this article. For Android 6 and higher, follow the instructions.
Android phone number unblocking
Here’s how to restore calls and texts from a blocked number on an Android device:
Get the Phone app open.
The More icon, which resembles three vertical dots, should be tapped.
Select Blocked Numbers under Settings.
The contact you want to unblock has an X next to it.
On an iPhone, how can I unblock a number?
On an iPhone, go to Settings > Phone > Blocked Contacts, slide left on the contact, and then select Unblock. Tap Settings > Messages > Blocked Contacts > Swipe left on the contact > Unblock to unblock numbers that are not in your contacts.
Can I have my phone number unblocked from someone else’s phone?
To get your number unblocked, you need to have physical access to the recipient’s phone. So, no, you can’t unlock yourself from someone else’s phone if you don’t have actual access to it.