In the tweaks of the Phone app is the list of blocked numbers.
Instructions apply to Android 6 and up.
This makes it easy to unblock a number so you could start getting calls and text messages again.

Here’s how to find this list and unblock the number:
Open thePhoneapp.
Tap theMoreicon, which looks like three vertical dots.
TapSettings>Blocked numbers.
Tap theXnext to the contact you want to unblock.
You must have physical access to a person’s phone to unblock your number.