1
If you see an Office icon on your Start Menu, if you right click it, do you get the uninstall option, or just the option to 'Unpin from Start'?
If you just see the 'Unpin form Start' option, not uninstall, then that app is not installed on the PC, it is just its icon available to start the free trial.
2
Otherwise, try using this tool from Microsoft to completely uninstall any previous Office version form your PC.