I bought Microsoft Office 365 and now it doesn't work. It says it is an unlicensed product. What should I do?
The first thing I would like to recommend trying is the official page related to Activation of various Office 365 versions.
Microsoft Support: https://support.office.com/en-us/article/Activate-Office-365-Home-Personal-University-Office-2013-or-Office-2016-1144e0de-e849-496e-8e33-ed6fb1b34202
If after you tried all the options still says it's invalid, then contact Microsoft and explain the problem. They will check your license status and provide further support in order to overcome this issue.