British gas owner Centrica saw shares plunge over 17 percent on Thursday, after the company lost almost a million customer in just four months.

Its share price sunk to its lowest level in 14 years, after losing 6 percent of its customer base in the period from July to October. The company also warned that full-year trading may come in below forecasts, despite raising its prices for millions of customers in September.

A one-off charge at the company’s North American units will send their profits down by £140 million for the full year, with stronger competition in the UK meaning the company are likely to just break even for the full year.

Centrica’s chief executive Iain Conn said: “Although some aspects of our delivery in the second half of 2017 have been disappointing, I remain encouraged by our progress in implementing our strategy.”

Investors were less encouraged by the performance however, with shares currently trading down 16.90 percent at 135.79 (1056GMT).