A little speed issue with my ISP

This problem is weird..... I cant get my head around it.

I have been through several different speeds with my present datastream ISP
(joined them in Jan 2004), from 256kbps - 512kbps - 1mbit, then when my ISP
offered to trial me with ADSL Max, I junped at the chance and signed up to
trial the service. I had no idea when the trial would start, but one
morning I woke to find my speed was noticeably faster than I had been used
to. I quickly did a speed check to reveal I was now receiving 2032kbps
(2meg). I logged into my router and saw it was now syncing at 3776kbps,
instead of the normal 1mbit sync rate. Even the upstream speed had increased
from 276kbps to 832kbps. Great, it seemed that my ADSL Max trial was
underway!

For about three months the trial went on and I continued to get 3776kbps
syncs reliably and a 2mbit download speed, despite my monthly charge staying
the same as for 1mbit service. After the ISP offically launched ADSL Max I
got an email saying congratulations, I was now on ADSL Max (up to 8mbit).
My monthly charge increased to take into account the higher speed and I was
now paying for ADSL Max, according to my regular monthly bills. Even my
most recent bill says that the service is ADSL Max and the charge is the
right price for this sevice.

Yesterday I went to my ISP's website and clicked the sign up button, it went
on the say it needed a phone number to check what speed could be offered to
me, so I entered my phone number (the same number that has been running ADSL
Max for many months) and it came back with the following response: We are
sorry, but your phone line is not able to support ADSL Max. Well that can't
be right can it? I have already been getting ADSL Max (and being billed for
it) for almost a year!

I am wanting to call the ISP to clear this up, but I am concerned that their
incorrect records may force them to downgrade my service to a lower package.
According to the BT website, that is still confirming that my line is good
for 3.5mbps or greater, but according to my ISP's records I cant even get
ADSL Max on this line.

Even though my line commonly syncs at 3776kbps, the maximum data throughput
I can achieve has always been around 2000kbps (certainly no more than this)
and that is why I wanted to contact the ISP. I reckon with a good regular
sync at 3776kbps I should be getting slightly more than 2000kbps? Does that
sound right?

What do you experts have to say on the subject?. It would be nice to have
some opinions on my experiences.

How come the ISP website is saying I can't have ADSL Max, when I am actually
already getting it?

BT Wholesale ADSL Checker confirms my line is good for 3.5mbps or
greater....

And what is really weird is the fact that up until a few months ago, even my
ISP's own checker said I could get ADSL Max... Whats going on?

I believe my speed is being capped at 2000kbps even though the line will do
more than that.

Over to you guys.

Steven