Vodafone ads featuring actor Martin Freeman have been banned by the watchdog for including misleading claims about broadband speeds and bill reductions.
The TV and radio ad claim: "Vodafone guarantee your home broadband speeds or money off until it's fixed".
But consumers and rival BT challenged the claim in the advert, saying it could not be justified.
The Advertising Standards Authority agreed, and told Vodafone the ads could not appear again in their current format.
The ad in question featured Freeman playing a video game which cuts out at an important moment. Another player in the game tells him to "get Vodafone" before text tells the viewer they can claim a discount if speeds are below certain thresholds.
However, the advertising watchdog said the ads could be interpreted to mean Vodafone are guaranteeing speeds fast enough to carry out activities like playing an online video game.
In a statement, Vodafone said it was "disappointed" by the ASA's decision, adding it had "misunderstood" the offer.
"Our customers will continue to be offered this guarantee," a spokesperson said. "However, we will amend our advertising to take into account the ASA’s views.
"Our guarantee is still unmatched in the market as no other major brand offers a promise like this across their entire range, nor do they apply discounts directly to customers’ bills if they don’t deliver."
Vodafone also took the change to take a swipe at rival BT. "We note that BT is one of the complainants about this advert," the spokesperson continued.
"Given Vodafone’s home broadband service is the fastest growing service in the UK this is not surprising, but we suggest it might be better if BT focused on fixing the underlying problems of network connectivity."