Link to Worldpay suddenly not working

[scumblegoosie]

my shopping cart on www.englishpanelling.com is not very user friendly but has always worked until suddenly it stopped connecting to Worldpay on Friday. It seems the main issue is that the shipping address is not automatically copied to the billing address but I am not very techie so I could be wrong here! We have not made any changes so I am puzzled as to how it broke in the first place! Any advice gratefully received!  Ideally I want to fix the cart asap but then upgrade the cart altogether as it has never been easy to use and looks quite dated to me now.