Netmemo stores it's files in a folder that's typically removed by Android if you uninstall Netmemo. This folder is located here:
Or, if you're using Netmemo Plus:
Note that Netmemo does regular house-keeping in these folders (removes old files), so you don't have to empty it yourself.
Here are a few things you can try/check:
If Netmemo did not work on your device, please contact us. Don't forget to mention what device and which version of Android you are using. We will do our best to resolve all problems promptly.