I can understand the frustration caused here but regardless of what the Plusnet agent has advised and what they think we should do - we can only advise and do of what we know how to and that is for the number to be active on the account - to port, both Operators require certain technical details that are available when the number is active and we use this information and other details for security when porting across networks.
We advise that where a customer wants to port, they should always contact the new Provider and we will initiate the port request and cancel the telephone line on your behalf. Once the number has fully ported to us, you may contact the old provider to check and cancel any remaining services you may have with them. For more information, please see the Cease and Provide section following this Ofcom link - https://www.ofcom.org.uk/advice-for-businesses/switching/switching-landline
Cheers,
Ryan.