We get it. Doing it via physical mail is only adding time and the potential for errors to the process. The process is setup for online action. The CZ office in London is a ticketing office. Once received it will/should be sent on to the customer service center. You should bypass the middleman.
China Southern Ticketing Office, World Business Centre Two Newell Road, London Heathrow Airport Hounslow, Middlesex TW6 2SF, London, United Kingdom
I am trying to find their UK address to send them a letter to make the initial claim...