Telecoms operator TalkTalk has been fined £750,000 by the regulator Ofcom for making an excessive number of abandoned and silent calls.
In total the company made about 9,000 silent or abandoned calls to potential customers in 2011.
They were made through two call centres during a telemarketing campaign to attract new subscribers.
TalkTalk said it had terminated its relationship with those businesses as soon as the problem was discovered.
Ofcom said TalkTalk had exceeded the limit for such calls on four separate occasions in a seven week period.
Abandoned calls occur when a person answers the phone, but the caller then hangs up.
A silent call is where the phone rings, but there is only silence on the other end of the line, and no information message is played.
Ofcom said such problems were often caused by answer machine detection (AMD) technology.
Sometimes the software mistakenly identifies an answer machine or voicemail, and terminates the call, even though it has been answered by a human being.
"Silent and abandoned calls can cause annoyance and distress to consumers," said Claudio Pollack of Ofcom.
"Companies must abide by the law and Ofcom's policies. If they fail to do so then Ofcom will take firm action," he said.
TalkTalk said it was fair that Ofcom had imposed the fine, and blamed the two call centre operators concerned, Teleperformance Limited and McAlpine Marketing Limited.
It said it was in the process of recovering the fine from them.
"TalkTalk demands high standards from the companies it works with and as a result TalkTalk immediately stopped using these suppliers," said a spokesperson.
Last year, energy firm Npower was fined £60,000 by Ofcom for a series of abandoned calls which were made in 2011.
Two years ago the maximum fine for abandoned calls was raised to £2m.