The following bundle statement from the web site offer (
http://allyours.virginmedia.com/html...ers/vplus.html) is your catch but they really should have had this stated in the direct mail as well. As a current customer you need to add a service to get the £75 offer, it doesn't have to be XL TV according to what is said below.
The text on the web site today doesn't state the 3 for £30 bundle being excluded although I have heard this several times. One trick I would recommend therefore is to buy it online for which you will need your account number and your password, go through all the options selecting the option to keep your current service then under TV Extras select the V+ service add-on. The issue then is whether you ordered at £75 as I am not sure it actually states then when you go through the order.
Bundles: Available to new customers and existing customers taking an additional cable service (subject to status and credit checks).