A premium rate phone line company in Bristol has been fined £300,000 by the industry regulator.
Five prize claim line services run by Consumer First Marketing had generated 670 complaints, said ICSTIS.
The company blamed "rogue" companies to which it has supplied the premium rate numbers, but said it would now "cut" these numbers from its services.
Consumer First was banned from operating premium rate competition services for a year.
ICSTIS said automated messages were left on landlines under five different promotions: Cruise Connections, Globaltel, National Unclaimed Award Fund, CF Marketing and Caribbean Cruise.
The company had breached its code of practice in several ways, and had failed to provide all the relevant information when asked, ICSTIS added.
Rob Dwight, from ICSTIS, told the BBC: "The fine reflects the severity of the consumer harm caused."
Hopeful callers were unaware of how much their calls to claim prizes were costing, and Consumer First had failed to state how many prizes there were, if any at all.
The company had also made unsolicited automated calls, including to people who had registered with the Telephone Preference Service, said ICSTIS.