GMTV managing director Paul Corley said he was "shocked and angry"
GMTV has promised to reimburse viewers who are found to have entered its phone quizzes but had no chance of winning.
BBC One's Panorama alleged actions by the firm that handled GMTV's quiz meant thousands of callers were defrauded.
The programme claimed Opera Interactive Technology, which ran the contests, finalised shortlists of potential winners "long before" lines closed.
A GMTV news report said viewers would get their money back but it did not yet know how many were affected.
Panorama estimated that £10m a year was being spent by callers, but as many as half had no chance of winning.
GMTV has terminated its contract with Opera after finding "irregularities" in the company's procedures.
Opera earlier denied the Panorama claims and said it would hold an investigation.
GMTV managing director Paul Corley appeared on the programme on Tuesday to apologise and tell viewers he was "saddened, shocked and angry".
We will do everything in our power to make sure people get a refund and get reimbursed
"We set up a team we thought we could trust and frankly we were let down," he said of the relationship with Opera.
"We need to go through the back systems and find out exactly who wasn't counted in the competitions.
"We will do everything in our power to make sure people get a refund and get reimbursed.
"We will not bring back our competitions until we are completely sure we have another telecoms operator that is not going to fall into this trap."
Premium rate phone line regulator Icstis has requested evidence from Panorama and said it would also contact GMTV and Opera.
Opera released a statement on Monday saying it had recently improved procedures to ensure all contestants were considered "equally and fairly".
Opera had not "benefited financially from any errors in procedure in the past", it said, and had "removed relevant staff from normal duties with regard to GMTV competitions pending further investigation".
GMTV has promised to reimburse viewers who are found to have entered its phone quizzes but had no chance of winning.
BBC One's Panorama alleged actions by the firm that handled GMTV's quiz meant thousands of callers were defrauded.
The programme claimed Opera Interactive Technology, which ran the contests, finalised shortlists of potential winners "long before" lines closed.
A GMTV news report said viewers would get their money back but it did not yet know how many were affected.
Panorama estimated that £10m a year was being spent by callers, but as many as half had no chance of winning.
GMTV has terminated its contract with Opera after finding "irregularities" in the company's procedures.
Opera earlier denied the Panorama claims and said it would hold an investigation.
GMTV managing director Paul Corley appeared on the programme on Tuesday to apologise and tell viewers he was "saddened, shocked and angry".
We will do everything in our power to make sure people get a refund and get reimbursed
"We set up a team we thought we could trust and frankly we were let down," he said of the relationship with Opera.
"We need to go through the back systems and find out exactly who wasn't counted in the competitions.
"We will do everything in our power to make sure people get a refund and get reimbursed.
"We will not bring back our competitions until we are completely sure we have another telecoms operator that is not going to fall into this trap."
Premium rate phone line regulator Icstis has requested evidence from Panorama and said it would also contact GMTV and Opera.
Opera released a statement on Monday saying it had recently improved procedures to ensure all contestants were considered "equally and fairly".
Opera had not "benefited financially from any errors in procedure in the past", it said, and had "removed relevant staff from normal duties with regard to GMTV competitions pending further investigation".