Someone recently gave me this number for the UK:
Windows Live OneCare billing team on 0800 587 2920 (UK)
It would normally be used to cancel a subscription, but I suspect that it will also work to sort out other billing issues. You should *not* be charged anything for a OneCare renewal right now. If your susbcription is due for renewal, you should be offered a free 6 month extension. Check that out by signing in at https://billing.microsoft.com with your subscription LiveID and see if that is offered to you. If so, take it and you will not be charged and you won't have to call anyone. Note that OneCare is close to being unavailable for sale at retail and online, though new susbcriptions and renewals will be allowed for a while longer. Morro is coming soon and it will be free - see the announcement at the top of the forum.
The official path to support:
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator