Hello
timpuk Welcome to the customers helps Vodafone's community.
I will try to write it in English but some words are easier to put in Dutch.
Go to
My Vodafone account and go to INSTELLINGEN (in the Menu), and then click on MY VODAFONE ACCOUNT. A new window will open. There you see: JE ACCOUNT UITBREIDEN, click on it.
Here you can add a new Vodafone account to click on: VODAFONE TOEVOEGEN
This will help you to add a second account on your account, that you have already.