How can I get message from BT Synergy 2150 Answerphone?

My answerphone has broken. Tried new battery, which is showing the phone as fully charged, and "new msg" is flashing, but going through the options to retrieve the message it just goes back to the "new msg" sign, ie it won't play messages back.

I've got a message on the machine that I really want to keep. It's not the phone I'm bothered about as I've bought a new one, but I'd love to get that message out of the phone.. Can anyone help?