Who I have the same questioned this topic

Phone: Samsung S7

App: Verizon Message+ - all of the messages are on the phone and were sent using this app.

Backup apps don't work to download all of the messages.  For some reason many are left out.  When I try to print online it only gives me a limited amount of time that I can print from.  I can't seem to view older messages with the online app in order to print them out.

I tried downloading the file from the phone but it's in xml format and a hassle to try and format it to something readable.

How do I go about getting all of the messages from one contact?