Is your address completely correct on Royal Mail database
What is the issue with your address then, as I assume you have a working phone line?
It seems your address is still on Silver key over Openreach and we only have access to Gold Key lines over Openreach. That is the reason your address is not in the list on the website. Here, you have to visit the nearest Vodafone Store and they will contact Openreach and get your lines upgraded to Gold Key. (You don't have to pay anything for that).
The issue matched the thread I originally posted in.
That would have been a solved thread. As this needs to be dealt with separately, please can you explain the problem?
Are you moving from BT Retail to Vodaphone?