Ensure you don't have a Focus mode active that is filtering out specific people or groups.
If you’ve unblocked a number but still aren't receiving calls, check these secondary settings: how to unblock number iphone
If the conversation is gone: Go to → Messages → Blocked Contacts → Edit → Unblock. Ensure you don't have a Focus mode active
From here, you can unblock anyone by swiping left or tapping Edit. how to unblock number iphone