Getting USB devices to connect to the guest OS in VirtualBox can be a bit tricky. I run it on Windows so it might work differently on Linux, but anyway…
The key is to understand that in order for the device to be detected it has to be connected while the guest OS is running. If it is connected before it is started then it won’t attach. It will say it is, but it won’t be seen by the guest OS.
This small but vital fact is not made clear in the documentation.