The company behind telephone quizzes on breakfast TV programme GMTV has admitted "certain irregularities" and apologised to viewers.
GMTV managing director Paul Corley said he was "shocked"
Opera Interactive Technology said it would co-operate with GMTV and regulators Icstis and Ofcom to ensure competition entrants were compensated.
The company added it had put "systems and processes in place to ensure that this can never happen again".
The BBC's Panorama programme found some quiz entrants had no chance of winning.
Opera's statement said: "Investigations have shown certain irregularities in our internal processes which should have prevented anything like this from happening.
"Opera Interactive unreservedly apologises to GMTV and any of the competition entrants who have lost out as a result of any irregularities."
GMTV has also promised to reimburse viewers who are found to have entered its phone quizzes but had no possibility of being selected.
Panorama claimed Opera finalised shortlists of potential winners "long before" competition lines had closed. The show estimated that £10m a year was being spent by callers, but as many as half had no chance of winning.
GMTV terminated its contract with Opera after finding "irregularities" in the company's procedures.
The broadcaster's managing director Paul Corley appeared on the programme on Tuesday to apologise and tell viewers he was "saddened, shocked and angry".
"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".