On the porting day, it is fairly common for some UK networks to be able to call your number while calls from other networks fail, go to voicemail, or reach the old provider.

This happens because the original range-holder is responsible for setting up onward forwarding of your numbers to your new provider (or their provider) and when they have many interconnects, and routing hosts this can take time to propagate. 

NOTE: The original range-holder will always be responsible for routing your calls, even after you've ported to another provider. 

Typical symptoms include are that calls from one network work, but another cannot connect

It should normally settle during the porting day, though occasionally it can take until the following working day. It can take much longer for CNAM records to update but that will not affect call delivery. 

If calls from particular networks are still failing after the port should be complete, contact your new provider (if WE are your new provider open a ticket at the HelpDesk).

Give them:

• Your number
• The porting date
• The networks from which calls fail and if possible from what test numbers
• Approximate times and any error message callers hear

They will need to escalate this to their carrier, who will escalate this to the range holder and get this resolved.