This is generally done by e-mail, so you'll need to
include our e-mail address (support@exch.cx) in CC (this is mandatory to claim the reward).
Shouldn't this be BCC? It sounds like you're "brute-forcing" reports on the abuse email addresses. It is of course ridiculous that one valid report isn't enough to take action, but if they think of your brute-forcing as spam, it's going to be very easy to filter and delete the emails if they all CC the same email address.