And last year, resolution service the Energy Ombudsman received more than 1,000 complaints relating to energy refund requests alone.
Consumers have become so frustrated they have taken to social media to name and shame the firms responsible.
One social media group directed at supplier Utility Point has more than 300 members.
The page - called Utility Point Owes Me A Refund! - encourages posters to share information and advice on how to get their money back.
But Utility Point is not an isolated case and readers signed up to a range of suppliers - both small and large - have complained that energy providers are holding on tight to credit balances.