Vodafone has reported an annual loss of 6.1bn euros (£5.2bn), due partly to a big write-down in the value of its Indian business.
The mobile phone giant, which operates in 26 countries, wrote down the value of its Indian unit by 3.7bn euros after a major price war broke out last year.
Vodafone also admitted it had suffered a disappointing year in the UK.
Chief executive Vittorio Colao said a £4.6m fine from Ofcom was “the worst moment” for the firm and its customers.
The fine was imposed due to “serious breaches” of consumer protection rules, which led to customers losing money.
The problems were caused by errors linked to the company’s move to a new billing system.
Mr Colao said on Tuesday: “The operational issues are essentially resolved. I don’t call it rock bottom.
“The worst moment was six months ago. Six to nine months ago we were receiving twice the number of complaints. I was personally receiving complaints.”
Despite Vodafone reporting the hefty loss, its shares rose 3.3percent to 218p as investors appeared impressed with a strong outlook.
Mr Colao said earnings were expected to grow, thanks to average revenues from contract customers stabilising.
The UK was one of the operator’s worst performing markets last year, with revenues dropping 17 percent and profits down 31 percent due to the weak pound.
By comparison, its Italian business saw revenues rise 2.6 percent and profits jump 10.6 percent.