Almost 400 investigations were opened by the Energy Ombudsman into Economy Energy in November 2018.
Matthew Vickers, chief executive and chief ombudsman at the Energy Ombudsman, said the ombudsman had seen a “significant increase” in complaints about the energy company, which Ofgem has banned from taking on new customers.
Vickers said 399 investigations were opened into the Coventry-based energy supplier in November, compared to just 112 in January of the same year.
He added: “Common issues include disputed account balances, failure to issue refunds and concerns over billing delays.
“It’s really important that consumers are made aware of their right to bring unresolved complaints to us.
“It’s also important that businesses implement our decisions in full and put things right for their customers.
“On the back of information we have provided, Ofgem has identified that Economy Energy urgently needs to address both of these areas.
“We are keen and ready to work with Economy Energy to help improve its complaint handling and customer service, as we are with all energy suppliers.”
The ombudsman’s comments follow the news that the supplier has been banned from taking on new customers for at least three months.
Alex Neill, managing director of home products and services at consumer group Which?, said: “Economy Energy rated poorly in our most recent annual customer survey.
“Energy customers shouldn’t have to suffer shoddy service, billing and payment problems, or poor complaints handling, so it’s right that the regulator is stepping in.
“The company must now ensure it improves for the long term otherwise the regulator will need to go further to protect consumers.”
Economy Energy also scored poorly in the most recent customer service rating table from Citizens Advice. The supplier scored just 2.4 stars out of five.
Meanwhile in December 2017, Citizens Advice revealed Economy Energy finished bottom of its league table of energy suppliers for the second consecutive quarter.
The firm received a score of 1.8 out of five for its customer service for the period from June to September 2017.
Industry regulator Ofgem recently announced the supplier was under investigation and was one of the 14 companies which failed to pay its renewables obligation (RO) by the 31 October 2018 late payment deadline.
Economy was shown to owe £15,650,999.63 in RO payments and £1,413,304.97 in RO Scotland payments.
According to Companies House, Economy Energy has extended its accounting reference period from the end of March to the end of September last year. The company’s next set of results is now due by 30 June 2019.
An industry source previously told Utility Week that the sudden change could be a sign the company is facing financial difficulties.
A statement published on Economy’s website towards the end of last year said: “In response to the recent speculation and circulating misinformation, we would like to provide assurance that we at Economy Energy have no intention of closing our doors.
“We will pay our outstanding ROCs obligation in full, business will continue as usual for our customers.
“We would like to thank customers for their loyalty and continued support.”