Hello Jackie,
Your best bet might be to take your phone to an apple store for assistance.
Please make sure your phone is up to date, the do the following to make sure you haven’t accidentally blocked your friend.
“To unblock a phone number, contact, or email address, swipe left over the entry, then tap Unblock.” Have a look at the ‘Manage your blocked phone numbers, contacts, and emails’ section of the link we posted previously for more information.
Additionally,
Are you able to text any other contacts that are using the same carrier as your friend?