You need to delete the preference files. Applications will leave behind preference files, and sometimes application support files, neither of which are stored in application bundles.
Preference files can be safely deleted, but they usually take up negligible disk space - and, if you decide to reinstall the application again later, keeping the preference file means your settings will still be there.
They are stored in the Preferences folder within your user's Library folder (~/Library/Preferences), or may also be stored in the system-wide Library located at the root of the system volume (/Library/Preferences/).
Also, third party uninstallers exist which will search for these preference files for you, the most notable of which is a program called
AppZapper or AppTrap.
If it is saying that you need to purchase and the 14 day trial is over then all of the files within the application have not been removed.