Unfortunately that is correct. I learnt it the hard way when I was with them and I too got the same responses from PN. They initially implied my equipment, exchange and all sorts of things could be faulty and then checked if I had been wrongly profiled on their system and traffic management. Not once was traffic shaping even mentioned to me. I then did a search for P2P on the portal and learnt what traffic shaping and throttling meant. I started asking questions - easy ones were answered by staff and then the more difficult ones went completely unanswered.
The best way I can describe it to you is with this link:
http://www.plus.net/support/broadband/network/broadband_bandwidth_usage.shtml?pn_session=34151a2236d39cea05550288a263139b
The second graph is the total bandwidth PN have bought and it shows how they distribute it to their customers. When more people are using hhtp, email and gaming there is less for P2P and when the same people go to sleep there is more available for downloading. That is fine if you want to use it in this manner so try downloading at night as it might cure the problem.
From my perspective I was given a peak time allowance that I could not use for Usenet/P2P no matter what I did because PN didn't and don't have enough peak capacity for the number of subscribers they have. I didn't like the fact that I was being forcibly told what protocols and programs I could use at different times of the day because an allowance is an allowance and how I used it was for me to decide & not PN. PN also believe in buying traffic shaping equipment (cheaper) than more bandwidth as most ISPs do. They then crammed on as many people as they could and tried to squeeze out every last drop. There is no margin in their network and hence why the first graph displays what information they are dropping/discarding from reaching its destination.
If you are happy to do your downloads late at night i.e. 3am then you could be OK with PN otherwise find some good ISP as there are many still out there.