how do unblock numbers previously blocked

See the Manage Blocked Numbers in this support document. Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch - Apple Support go to the Blocked list and you can delete the phone number and/or email address.

Thank you, but we are not really Apple Support. Just so you understand, this is a user to user support forum and Apple does not participate here. We are users, just like you, and we voluntarily read the forums here and offer help to users based on what we have experienced. We will also provide links to Apple Support documents that provide troubleshooting tips as well. Glad this helped you and you are satisfied.