Well an engineer and the manufactures saying the same thing. What do you think?
Sounds like the code has been locked, without a nvm reader your stuffed.
£250 isnt a bad price TBH  is it a straight swap over?
If your brave enough go to my friends website 
http://www.securitywarehouse.co.uk/catalog/index.php?main_page=product_info&products_id=322
Buy the whole panel and keypad for £34.19 change it yourself.
                
 Alarm
                
 January 2011