OK I'm going to cut and paste all your information in one document and bring it home for hubby to analyse and get going with this... i had no idea there were so many knowledgeable folks here!
last night we started recording the access log through our router to see if any MAC addresses showed up besides our two. So far nothing, but we will give it 48 hours to be sure (the last bill showed pirate activity every single day but maybe they are skipping days right now?). If we still see nothing then we're in deep doodoo
and will have to consult a specialist to get this resolved... luckily we got connected with a Pro last night who can help us (thank you mesaana!), he will lend us the cables and splitter for a couple of weeks for the test, and then it's a process of elimination, I guess.
All this crap started happening around early August, there were no problems before that. Maybe a netpirate moved into a nearby building in July, who knows? Could it be possible that Videotron is somehow responsible or involved, ie mis-calculating our daily usage?
of course they say "no way" and are not interested in helping us, either...
i wouldn't wish this on my worst enemy. feels like a home invasion and feeling so helpless to stop it!