Shares in TalkTalk have tumbled more than 10% after the firm warned that profits would be significantly lower this year than previously thought.
TalkTalk also announced plans to raise £200m by selling shares on the stock exchange and slashed its dividend.
The firm is raising money to invest in a network of fibre cables that would allow much higher broadband speeds.
However, this year it expects a key measure of profits to be between £230m and £245m.
That is much lower than its forecast made in November, when it expected the same profit measure to be between £270m and £300m.