Bummer. I had one break exactly there on a bump on an out-of-warranty Ortlieb. I tried to fix but ended up buying a replacement--not expensive here in U.S.
Have you tried phoning the distributor there? I've always found Ortlieb people to be very responsive here in the U.S. They've sent me free replacements on some stuff without even confirming if it was under warranty.
Also maybe try eBay and see if they will ship. Here's a listing for that lower hook.