I get the following error when upgrading to "Infinity 2" online, despite me having had Infinity since it arrived at my exchange a year ago!
This offer is only available to BT Infinity customers. Please visit www.bt.com/infinity to find out more.
I had the exact same error and it was because my Infinity and phoneline wasnt linked together so they had to do that before I was able to upgrade my speed, all in all it took about a week to do.
Had the same issue, this is how i solved it.
Try a different browser(used my ipad in this case) but do not log on to my bt and go directly to the upgrade link (http://www.productsandservices.bt.com/consumerProducts/displayTopic.do?topicId=29280) and enter your phone number and post code manually and whoala!
After you've completed the order it should appear on My BT normally.
Using IE instead of FF gave me the same error; I'll have to call from work today and see if I get anywhere 😞
Thanks for all the help.