The only way to retrieve messages that have been sent or received is to sign-in to your Textfree account using Textfree Web.
Once signed in, you can copy and paste all of your conversations into a word processing document such as Notepad or Microsoft Word. This is the only way to retrieve your message conversations at this time.
There are two reasons to explain why your messages are no longer in your inbox:
You manually deleted them while logged into your account
You’ve set a block, which will automatically delete any messages from your device