Robin Hood Energy has launched an internal investigation and suspended its chief executive and finance director.
Gail Scholes and Robert Bain are also no longer directors of the company, which is owned by Nottingham City Council.
The company has confirmed that three new senior executives have since been appointed, with former Orsted managing director Jeff Whittingham taking on the role of interim chief executive.
Mike Thomas, who was finance director at Eon between 2007 and 2011, becomes interim finance director, while former Co-op Energy chief executive David Bird has become a board advisor.
Robin Hood Energy refused to comment further on the nature of the suspensions.
A spokesperson for the company said: “We can confirm three new senior executives from energy backgrounds have been appointed to continue our mission of reducing fuel poverty and challenge the big six energy companies by putting people before profits.
“Due to an ongoing internal process it’s not appropriate to make any further comment at this stage.”
Meanwhile the supplier has also revealed it has until the end of March to file its accounts, after initially being given a deadline of 31 December 2019.
The spokesperson added: “With the appointment of three new senior executives it’s understandable that they needed time to review the accounts prior to submission.
“In compliance with Companies House rules we have changed our company year-end date, meaning our deadline for filing is now the end of Q1.
“Nottingham City Council, the board and our auditors all supported this decision and are working towards our new deadline.”
Towards the end of 2019 Robin Hood was revealed as one of several companies which owed regulator Ofgem millions in renewables obligation payments.
Nottingham City Council loaned Robin Hood £9.5 million in order to pay off its obligation.