Length of a Promotional Discount?

Have a look at your contract https://ebill2.virginmedia.com/ebill3/ViewContract.xhtml 

Hi Steve,

Also, if you pay by direct debit then you will receive a billing email each month which advises of the next amount due to be paid, along with information on promotional discounts and when they are due to end.

EDITED due to typos.

Mine has no dates - maybe its forever :-)