Now comes the first hard evidence that customers have voted with their feet - with 62,000 leaving the energy firm.
The David vs Goliath battle in which perseverance and patience literally paid off.
The Chancellor has urged energy companies to reconsider their price hikes, in an interview with ITV News.
npower received five times as many complaints as the best performing energy firm SSE, research showed.
- npower had 202.5 complaints per 100,000, compared with 38.3 for SSE - the lowest level of the main energy providers - from the April to June period, Consumer Futures research showed.
npower also recently announced a 10% average bill increase but has said that it will reduce bills as a result of a shake-up of Government green levies.
– Sarah Harrison, Ofgem senior partner
Many npower customers will have noticed a serious deterioration in service levels over the last year.
The huge growth in complaints about npower is wholly unacceptable and is an issue that Ofgem takes very seriously and is why we intervened in this case.
npower's commitment that its customers will not lose out financially as a direct result of the company's billing system problems is important and we will expect npower to do all it can to identify and rectify such cases.
npower's chief executive has apologised "unreservedly" after billing errors affected thousands of customers.
Paul Massara wrote in a letter to npower's 3.4 million customers: "We've let many of you down recently in the overall levels of customer service we've been providing. We apologise unreservedly."
He said the billing problems arose after customer details were transferred on to a new computer system. Around 700,000 customers are thought to have been affected by the problems, though it is believed the vast majority are not financially worse off.
Mr Massara said the issue was being dealt with as "our top priority", and hundreds of staff were working to address it.
Many customers affected had already been contacted individually to address specific problems and others would be, he added.
Gas and electricity supplier npower has written to its 3.4 million domestic customers and donated £1 million to vulnerable consumers after billing errors led to it being the most complained-about energy company.
Regulator Ofgem said there had been a "serious deterioration" in customer service levels after the German firm admitted a glitch had led to a number of errors.
The errors included; a number of bills and statements failing to go out on time, direct debit payments not being set up properly and some customer accounts having problems being started
npower chief executive Paul Massara said that anyone affected would not lose out financially as a result in his letter to customers.
Ofgem said it had been increasingly concerned about npower's customer complaint levels, which have risen sharply in the last year, but welcomed the apology and payment.
Labour MPs have criticised the "irresponsible behaviour" of energy giant npower after it announced job cuts affecting 1,460 workers in the UK.
Stoke-on-Trent North MP Joan Walley said it was the "last straw" from one of the so-called "Big Six" energy companies.
Ms Walley's fears were echoed by her Labour colleague Tom Blenkinsop, who has constituents that could also be affected by the cuts.
Energy Secretary Ed Davey admitted it was a "very worrying announcement".
The chief executive of npower said its restructuring proposals aim to deliver a more "efficient, flexible and improved customer experience".
Paul Massara said in statement:
I understand that these changes would be incredibly hard for some of our employees and we’ll be doing everything we can to support them over the next few months.
This restructure is necessary if we are to deliver the levels of service our customers deserve.
We would have the flexibility to keep call waiting times down during busy periods, and continue to keep costs down so we can keep bills down.
Energy giant npower, owned by German company RWE, said its customers would continue to be served on the phone by people based in UK call centres under its restructuring proposals.
However, back-office functions would be outsourced to India, npower said in a statement.
Energy company npower has confirmed it is planning 1,460 redundancies in the UK as part of restructuring plans.
Under the proposals, the main impacts regionally would be:
- npower's offices in Stoke on Trent would close, affecting 550 employees
- One of three offices in Oldbury would close and around 400 face redundancy
- Around 430 employees face redundancy at Rainton Bridge, Sunderland
- Approximately 80 employees at npower's site in Leeds face redundancy
- npower's site in Thornaby would close, but all roles would be relocated to Rainton
- Although there would be no redundancies at the Peterlee offices, several teams will be moved between the Rainton and Peterlee offices
The firm said around 540 existing staff will be transferred to retail outsourcer Capita "to allow customers to benefit from the expertise of npower's existing employees".
Energy firm npower has confirmed around 1,460 staff members in the UK will be made redundant as more work is outsourced to India.
Energy giant npower is expected to announce plans to move more than a thousand jobs abroad and transfer hundreds of others to another company.
It is believed that:
- 1,400 jobs will be offshore to India and around 570 transferred to another company.
- The GMB union said sites at Peterlee, Stoke and Thornaby, near Middlesbrough will close.
- The expected news follows a number of cost-saving announcements from npower since its German owner RWE said earlier this month that *6,750 *jobs would be cut across Europe.