Virgin Media has seen five adverts for its TV, phone and broadband bundles banned by the Advertising Standards Authority (ASA).
The media regulator upheld a complaint from BT over the savings claims and offer expiry dates included in marketing material for its rival's Starter Collection.
In its ruling, the ASA said the broadband adverts had the potential to mislead members of the general public, and as such, must not appear again in the same form.
The regulator took exception to Virgin Media's use of the term "Offer available until at least…", which failed to specify an expiry date.
"We considered that wording was ambiguous and did not make the duration of the advertised offers clear, particularly in the context of ads that included prominent text that implied the offer was time-limited," the ASA stated.
It also agreed with a BT complaint over the reference prices used for broadband deals, since some consumers were never charged the full advertised price during their contractual term.
Virgin Media no longer offers the Starter Collection - consumers can now choose from a range of 'Big Bundles', including the Big Connection, Big Easy, Big Bang, Big Kahuna and Big Daddy.