I'm not sure exactly what your ISP promised you they could achieve with you using their quarantine box, but as AFAICT there is nothing you can do about the result. The offending spam simply gets quarantined (and presumably deleted after a fixed period if you don't do that manually), that's all.
If you don't like to see it, don't check that q-box. If important non-spam messages get dumped in there erroneously, you've got a problem for which the system doesn't offer a solution. After all, there is no way your ISP can stop spammers from sending spam, and as long as they do you'll see it in your q-box.
