hi there,
I'm going to assume that you've reached your last payment on your contract, sometimes our systems may take some time to process your bill and that may be the issue as to why you are unable to get passed that message.
to upgrade
you are more than welcome to go into one of our stores. (if possible and SAFE for you) and proceed to upgrade through our stores.
you can call 202 (from your phone) or 0344 809 0202
(from landline) to upgrade aswell.
thanks
will