Mobile broadband provider Three has been hit with a £250,000 fine for failing to comply with Ofcom's rules regarding customer complaints handling.
The media regulator issued the penalty - which is payable within 30 days - following an investigation, which came as part of its wider monitoring and enforcement programme.
Ofcom found that Three failed to handle some customer complaints in a fair and timely manner. They were closed without the broadband provider establishing they had been fully resolved.
In some other instances, Three failed to log calls from customers as complaints. This means customers were not entered into, or treated in line with, the firm's formal complaints process.
Additionally, Three did not make sure customers were sufficiently aware of their right to alternative dispute resolution - access to which is free of charge.
Claudio Pollack, Ofcom's Consumer and Content Group Director, said: "When things go wrong, customers are not only entitled to complain to their provider, but must have confidence that their complaint will be dealt with fairly.
"That's why we impose strict rules on providers on how they must handle complaints."
He said the regulator treats any failure to follow these rules "seriously".
Mr Pollack added that the fine imposed on Three takes account of the shortcomings in its complaints handling, but reflects the fact that harm to consumers was limited in this case.
Otherwise, the mobile broadband provider could have been hit with a much larger penalty.
"The company fully co-operated with our investigation and has now taken steps to ensure it's compliant with the rules on complaints handling," Mr Pollack noted.