Channel 4 is investigating claims that viewers were asked to ring a £1-a-time quiz on its Richard and Judy show, even though callers had already been chosen.
E-mails leaked to the Mail on Sunday alleged that the You Say, We Pay contest was being promoted on-air even after a winner had been selected.
The competition was dropped from Friday's edition of the teatime show.
Channel 4 said "something had obviously gone awry", and added it was committed to acting "fairly and transparently".
"We reject any suggestion that we would knowingly mislead viewers in any way," a statement from the broadcaster said.
"It makes no material difference to the channel whether the eventual winner is selected the moment the phone lines open or just before they close"
"Our contract with the service provider clearly states they must comply fully with the codes that govern competitions of this nature drawn up by [watchdog] Icstis."
The programme's producers, Cactus TV, also took the need to follow broadcasting codes "very seriously", Channel 4 added.
The premium-rate lines are run by service provider Eckoh, which uses a computer to pick 24 potential winners from the callers who ring within the first few minutes of the show going on-air.
The Mail on Sunday claimed it had obtained a copy of a message sent by Eckoh to Cactus TV timed at 1709 GMT last Wednesday, listing 24 names and numbers.
However, 10 minutes later, the programme once again invited callers to try their luck on the quiz.
Channel 4 denied it was making money from this process, saying that the overall costs of running the competition were fixed.
"It makes no material difference to the channel whether the eventual winner is selected the moment the phone lines open or just before they close," its statement said.
Neither Cactus TV nor Eckoh could be reached for comment.
Big Brother
It is not the first time that Channel 4 has faced scrutiny over its competitions.
Last year, Icstis ruled the network had breached guidelines during a telephone vote on reality show Big Brother.
Channel 4 invited viewers to select one of the evicted contestants to return to the programme.
But this prompted about 3,000 complaints from people who felt they had been misled when they paid to eliminate the housemates in the first place.
Channel 4 was not fined but it had to pay about £50,000 in administrative costs.
The broadcaster was also criticised by the Advertising Standards Agency twice in a month in 2006 for its "golden ticket" contest on the same series.
Anyone finding a golden ticket in a KitKat chocolate bar won the right to enter the draw to be a Big Brother housemate.
The watchdog said terms and conditions were not clear enough on marketing material, and an independent observer should have been present when the winner was picked.
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