Promises to do something are common, but little seems to happen, other than the abuse addresses going dead.
Generall, I accept that there is little you can do if the offender is not on this network, however two things would be useful:
First, and most important: If the reported eMail is indeed fake, which, if reported, it probably is, then verify this to the reported as quickly as possible. Warning that if any link has been opened on the fake eMail, that the account security will need to be updated.
Second, and yes, this is bells and whistles: It is useless for us to contact the mail handler of the fake eMail, as all our complaints will go straight into the trash. They will treat us no better than you do, and you do little better than trashing our complaints. You are in a position to blacklist any eMail handler which repeatedly conveys fake eMail. This threat from you will carry some weight, as it can put them out of business. We cannot do any more than complain to an unlistening ear.
Other people, like eBay, and paypal take serious interest in fake eMail, and do at least fulfill the first requirement. What other measures they take, I do not know, but at least they listen, and reply.
That is the very minimum to be expected, and if you persistently fail here, you will lose clients.
I will be interested in your response.