We are constantly working to detect when a telephone number has ported away. When we realize that the number has ported out, we automatically cancel the service on that number so you aren't continuously billed for it.
If you believe that your number has ported away and yet you're still being billed for it, you can cancel it yourself using the following article:
But be extra sure that the number has ported away before you remove it from your account. If you aren't sure, please feel free to contact customer support.