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Schools and businesses in Kent have fallen victim to a nationwide scam.
Fraudsters are posing as staff from the Yellow Pages and emailing invoices to schools and businesses in the county.
Trading Standards say the invoices look authentic and many are paying the bill without checking whether they advertise with Yell or who they are paying.
Marion Ward is from Kent Trading Standards: "What they are doing is sending you an invoice, often by email, leading you to believe you owe between £600 and £700 but actually you do not.
"We are asking business, schools and nursing homes in Kent just to check. Don't pay it just because someone says."
A spokesman for Yell said: "We take our responsibilities for consumer protection very seriously and as a responsible company are committed to supporting and protecting the users of our products and services and our advertisers.
"We don't hesitate to take legal action if necessary to protect our brand and safeguard our registered trademarks."