Next step is to Register the Sim...On your 48 Account page select 'My Sim' from the Choices to the left, then In the box 'Register Now'.
The Sim should be Active in 10 minutes...
This is confusing.
What do you mean?
How are 48 asking to update your details?
Are you sure that this isn't some sort of phishing scam or something?
If it's not and you are already in touch with 48 support then surely they can advise on what you need?
If you are already a 48 customer then can't you just log into your existing account, order a replacement SIM (if necessary) and then buy membership?
Hope this helps.