Tough decision and time it takes to resolve this sucks. The most effective way is probably to wage an expensive lawsuit. The bank clearly doesn't want to go to court since it would cost them a lot of money and HKMA to be on their butt on a lot of stuff, if they aren't already. Would advise hiring a lawyer with expertise in this area to handle your settlement negotiations. Should be well worth the money since right now they aren't even compensating you. The offer to roll back to what it was a while ago is pretty lame and a sign they are testing you.
hullexile brings up a good point and that's how much can they really give you. No returns are guaranteed. Giving back what was "stolen" seems a fair offer. Unless there is some cause for mental distress that can be quantified then I'm not sure what can be added on.