Unfortunately we have no influence on this. Sexjobs has no internal messaging system. All correspondence goes through its own mail servers. That means that e-mail traffic is directly between advertiser and visitor and not through Sexjobs. We don't see any reactions and can therefore not stop or forward them.
It may be that the advertisement(s) you respond to, have already received so many responses, that it is practically impossible for the advertiser to respond to them all. It's not nice, but it happens, unfortunately.
It is also possible that the advertisers e-mail has ended up in your junk mail. You might check the security settings of your own e-mail account.