Independent energy supplier, Economy Energy, has been banned by the UK market regulator from taking on new customers due to "unacceptable" services.
Ofgem said the ban would be in place for up to three months initially for Economy Energy to resolve its customer service issues, including complaints on handling processes and standards as well as billing and payment procedures.
Economy Energy has been told to improve its customer contact procedures via email and webchat, address billing and payment failures and issue customer refunds in a timely manner.
Ofgem can extend the ban if the company fails to make improvements within three months and can revoke the supplier’s licence if it fails to improve after that.
"Ofgem is taking action to protect customers from suffering more harm from the unacceptable level of customer service provided by Economy Energy," said Anthony Pygram, Ofgem’s director of conduct and enforcement.
"We expect the supplier to take immediate action to rectify its failings or face having its ban extended."
The regulator has been cracking down on energy suppliers over customer services and bills.
A new energy price cap came into force at the start of the month, saving 11 million people an average of £76 a year.