Just to double check -- what is your current setting for "Filtering Method" in "Call & Text Blocking?"
To block/unblock phone numbers, there two ways to do this: 1) Set "Filtering Method" to "Stop only blocked callers", and add any phone numbers you'd like to block in the Blocked List. Any number not in this Blocked List will not be blocked. 2) Set "Filtering Method" to "Allow only approved callers" or "Allow only approved callers and anonymous callers", and add any known phone numbers you do not want to block in the Approved List. Any number not in the Approved List will be blocked.
Please let me know if you're able to adjust the settings to remove the phone number from being blocked. Thanks.