Recovering text messages from iPhone 4S

So here's my dilemma: I was trying to get my text messages from my iPhone 4S transferred to my PC. One of the things I attempted to do was use iTunes on my PC to create a backup by choosing "Restore from Backup". So I connected my phone to the PC using a USB cable. When I ran the process, though, it ended up upgrading my iPhone to iOS 9.3.5 and it deleted all my texts from October 2015 to May 2018. I have tried all kinds of third party programs including Phone Rescue, Dr Fone, and Tenor Share. None of them reveal the missing texts. But they do indicate various dates that a backup was done, and May 20, 2018 is one of them. So I don't understand why the upgrade reset my phone as if October 2015 was the last backup. Looking for help on how to retrieve text messages, if it's even possible at this point?