The company is the second of the 'big six' energy providers to be fined for failings in the way complaints are dealt with. In July, British Gas had to pay £2.5m for the same offence.
The energy providers were found to be in breach of regulations introduced by Ofgem in 2008 which set out minimum requirements of what customers could expect when they complained.
But if you are unhappy with your energy company, how exactly should you go about complaining and what if you are dissatisfied with its response? Here are some tips...
How to make a complaint
● Your first port of call when making a complaint should be the energy provider itself. Check the company's website for details of its complaint procedure. There may be an online form to complete and you should be given information about how long you'll have to wait for an initial response.
Usually you should hear something within 48 hours.
If you are phoning the company with your complaint, gather together evidence of exactly what the problem is and supporting documents. This could include your account reference number, your contract, details and dates of when the problem occurred and any steps you have taken to remedy it.
Record the date and time of the call and be sure to get the name of the person on the other end of the line. If the dispute is minor, it may be resolved immediately.
However more complex complaints will need further investigation. Make notes during the call and ask exactly when you will be contacted and who will be calling.
Say that you will be following up the complaint in writing and keep a copy of your letter so you have evidence at a later date if the complaint is disputed. At the top of the letter state clearly that this is a complaint.
It's worth sending it recorded delivery and keep the postage receipt.
If the complaint can't be resolved or you are unhappy with the outcome, it should be escalated through the company in line with its complaints handling procedure.

● Should the dispute become 'deadlocked' and there is no resolution after eight weeks, you can then take it to the energy ombudsman who will investigate your complaint.
This is a free and independent service. The ombudsman can be contacted on 0845 055 0760 or at www.ombudsman-services.org
● If you need further help and advice on making a complaint, Consumer Direct is a Government-funded service which can give specific information on complaining to your energy provider, along with tools such as complaint letter templates.
It can be contacted online via the Direct.gov website (http://www.direct.gov.uk/en/index.htm ) or on 08454 04 05 06.
Please note: Any rates or deals mentioned in this article were available at the time of writing.
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