Google Play Store no longer updating/downloading

[AC Question]

I have a Samsung Galaxy s6, approx 5 months old. Up until a few weeks ago it's been working fine, but now I can no longer update and download apps via Google Play Store (I can download from other apps and browsers just fine, it's only Play Store that has issues). I've searched for others with the same problem, and I've found quite a few old posts about similar issues, however, I have no tried every single thing that has been suggested, and I'm at my wits end.

Things I've tried:

Rebooted phone
Tried a different wireless network than home
Disabled and re-enabled Google Play Store
Uninstalled and reinstalled Google Play Store
Uninstalled and reinstalled Google Play Store via APK downloaded on PC and tranferred to phone
Cleared Google Play Store cache and data
Cleared phone system cache
Reset phone to factory settings

After resetting to factory settings, I got some of my backed up apps back, but some didn't install, and now it's doing the same thing; sits on "downloading" and never actually downloads or installs. As a result of resetting to factory settings, I've now lost some of the old apps that I at least had installed before but couldn't update (Facebook Pages Manages, Outlook and some others).

Any help would be greatly appreciated!