System considers Office 365 Pro Plus as Office 2016 trial - Cannot activate

What does the following show:

cscript "C:\Program Files (x86)\Microsoft Office\Office16\ospp.vbs" /dstatus

In general you can remove any key/license listed there and reactivate. More info and script here:

https://blogs.technet.microsoft.com/odsupport/2015/05/01/how-to-reset-an-office-365-install-to-the-initial-activationinstall-state/

Marvin Oco: Where did you reinstall Office 365 Pro Plus from? Was it from here: https://portal.office.com/account#installs? If not, install from this link and activate using your Office 365 login credentials.