According to the CX forum, CX has modified its service and now routing flights differently, as well as making aircraft modifications.
http://www.flyertalk.com/forum/catha...n-no-more.html
BA/ExecClub/Avios must have accommodated you on alternative flights so you still have a valid ticket. The new service has business class albeit regional business have been a variable product in this part of the world, but even PE is certainly a step up for what passes as business class within Europe on most carriers, BA included. So not sure what the issue is other than CX has decided there's no benefit to doing a SIN stop enroute, a logical conclusion if it can do a nonstop ex-HKG, its base. So this may be an inconvenience to the OP since his/her party must now fly SIN-HKG and then on to Columbo, but pretty sure the party's been protected. Under such circumstances, Avios would take seats from revenue if no award seats remained on the flights.
OP should call ASAP to determine what they've been protected with. If this entails a cabin downgrade, then negotiate a rebate of a few thousand Avios miles per ticket. And post here so we know the outcome.