What exactly is up MK1, that they wouldn't upgrade you to 50Mbit free of charge?
It's not cheaper, not sure what makes you say that. It's 8 quid a month more taken with or without the phone line. I can only guess that the extra 10 pounds quoted is due to the 89.50 being a special offer of some kind.
EDIT: A quick read of your posts and I see why. You're paying 37GBP/month for 20Mbit at the moment, the price quoted now is actually 17GBP a month less at 20GBP when you take a phone line -
http://allyours.virginmedia.com/webs...uct.do?id=3246
That's where the discrepancy comes in, you're on an old tariff whcih doesn't have the 17GBP/month discount that is put on accounts now.
This probably belongs in Billing issues.