Most ops and/or voiced users in file-sharing channels are normally afk... I guess you're just going to have to patiently wait for a response. Bear in mind that some channels do not allow massive private messaging to ops (don't know why *shrugs*)...
As for how to address an op, they're no different to any other user (although some of them just luuuuuv thinking that way)... just be as polite as common sense tells you to be... oh, and yes, it'd be better if you address the problem right away ("excuse me, sorry to disturb your well-deserved resting time, but I happen to have this problem...")
Hope it helps
