The renewals system is broken, links don't work to renew servers from the e-mail you receive.
What you need to do is visit
www.ovh.co.uk/cgi-bin/order/renew.cgi and type in the hostname of your server (e.g. ksXXXXXX.kimsufi.com or nsXXXXX.ovh.net) then choose a renewal period.
Your server will be reactivated within 10 minutes of receiving payment. I recommend you do this right now, 3 more days and your server is gone!