I wouldn't put it past them. Some isp's can be total jackasses doing illmoral modifications of your bandwidth, but most likely they attempted to get absolved of all responsibility for basically anything whatsoever past what the law would be interpreted to insure, this is if your isps are like the ones in the U.S. Sooooo, what isp do you have? As well I would suggest you use different ports than the default, the easiest way I think is to just add a few thousand to the orginial ports, just change the thousands and ten-thousands digits, pick something up high randomly maybe around 30k or 40k, there is lots of random traffic in the unregistered port ranges for isps(I believe at least, it would make sense) as opposed to the cookie-cutter check your email and scratch your ass traffic that they are probably used to for port 80.
In conclusion, try what I suggested up there ^ and post back with the results.