Thread moved to Virgin Media Internet Services forum.
It's never a good idea to assume you know the answer when you pose the question, it may make you ask the wrong question. Like assuming you have a problem with the exchange being downrated or something.
The ADSLMAX product is indeed up to 8meg, with actual speed determined by line length and quality. I am on that product, through Virgin Media, and my router is normally locked on at about 3.5meg. Congestion normally prevents me getting more than about 2.7meg, even at off peak times.
However I constantly get letters from Virgin trying to entice me to move from their 2meg DSL product, to the up to 8meg product, 'for only one pound more, plus a Virgin phone package'. I used to be on their 2meg product, but moved quite some time ago. I have no idea what part of their systems think I'm still on that product, but the part that actually provisions the service doesn't think so as I am definitely on ADSLMAX.
If you can be bothered to do battle with India, you should eventually be able to persuade someone of your case, especially if you can produce proof of what package you were on (set-up emails, logs from speed test sites, that sort of thing), but TBH as others have said it may be as well to just give them the middle finger and sign up with someone else, especially if the exchange has been unbundled (mine hasn't, unfortunately, it's far too remote and rural).
At the very least, when you phone them to get your MAC code you will speak to someone in a UK call centre who might be more willing to take your complaint seriously.