[Sephiroth]

If you do call it in get them to look at your SNR. For the 256QAM modulation, you're right on the lower limit without any headroom for marginal conditions.

It may not be your modem that's causing the poor experience.

You can post your stats on the support newsgroup; they'll notice it's an old modem and offer the replacement, but will also test your line if you make the point.

151 might get you onto the offsahore call centre and although they'll happily arrange a new modem, they're not likely to want to understand anything about the low SNR.