If you have not given notice to Plusnet then they will bill you at out of contract rates for 14 days from the date that your number ports thus ceasing your relationship with Plusnet. See this page:
Not quite @jgb. Plusnet would be notified of the pending number port which would start the notice period, though that may only be a few days before the port.
Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.
