Your problem : Virtual Box keeps its folder and settings in your home folder. Delete everything inside the folder.
Uninstall VirtualBox first.
sudo apt-get remove --purge virtualbox
Run these commands to delete all virtual machines and settings and Virtual Hard Drives:
sudo rm ~/"VirtualBox VMs" -Rf
sudo rm ~/.config/VirtualBox/ -Rf
If you want to install it again. Run this command:
sudo apt-get install virtualbox
sudo ps aux | grep -i "vbox"
Kill any “ghost” processes you may think are relevant.
sudo pkill VBox*