True, they should have such responsibility. But AFAIK they do have the right to do whatever they want to your miles account for whatever reason, right? So maybe that extends to not giving a toss when they make a mistake.

Unless the fraudsters were travelling on fake passports, they should be pretty easy to trace (well, as easy as tracing people in West Africa can be). It may be that EK are waiting for the local police to do something.

Have you called EK again, recently? Don't they have an IO-only phone number that you can call? It is rather shortsighted of them to piss off a commercially important customer. You'd think that they would restore your miles first, and then try to figure out what happened to them.