TV hosts Richard Madeley and Judy Finnigan have apologised to viewers for problems with a quiz on their show.
The quiz has been suspended until Channel 4 has investigated
It follows claims that callers were told to phone a premium rate number even after contestants had been chosen.
At the start of Monday's show, the couple said they were "shocked and angry" about the matter and those affected would get refunds.
Channel 4 has launched an investigation and said it would not "knowingly mislead viewers in any way".
The presenters added that they were unaware of the issue until Friday and the You Say, We Pay quiz would be suspended until the investigation was complete.
Premium rate phone regulator Icstis has also launched an investigation.
Icstis said it would look into the matter as quickly as possible, owing to the "big public interest" in the allegations.
Finnigan opened the show by saying: "Many of you will have read over the weekend and today that some problems have come to light with the You Say We Pay competition.
"It seems some callers have not been properly entered into the competition."
Madeley continued: "A full investigation has been launched to find out exactly what's happened, and we won't be running You Say We Pay for the time being. "
"Once we know the full extent of the problem, we'll be making arrangements for any viewers affected to get their money back."
Finnigan added: "Richard and I knew nothing about this until late on Friday afternoon - we were very shocked and also angry on your behalf. We're very sorry."
The Mail on Sunday claimed leaked e-mails showed that the quiz's premium rate entry line continued to be promoted after a contestant had been selected.
Icstis spokesman Rob Dwight said the regulator would ask to view the evidence that led to the Mail on Sunday article.
It will also talk to Channel 4, production company Cactus TV and Eckoh, the provider of the £1-a-time phone service.
"As a consumer protection body, we have a duty to investigate all complaints, so that is what we will be doing," Mr Dwight said.
"We are gathering the hard facts and will take a decision based on what that evidence shows."
He added that investigations usually took about eight to 12 weeks.
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.
Big Brother got into trouble for bringing back evicted housemates
But 10 minutes later, the programme again invited callers to try their luck on the quiz, the report said.
Channel 4 said it was investigating to determine the extent of the problem.
A spokesman said full refunds would be offered "if it's found that viewers have been encouraged to enter the competition after the cut-off point has passed for selecting a potential winner".
"You Say, We Pay will not be broadcast as part of Richard and Judy tonight and will not resume until the channel has completed its investigation into how the competition is being run," he said.
Last year, Icstis ruled Channel 4 had breached guidelines during a telephone vote for reality show Big Brother.
The broadcaster 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.