Those of you who do not have PayPoint terminals will probably find it irritating that I write so often on the subject on the other hand, those of you who do have terminals, take good note of the following.

This is a warning from Chetna Patel, who runs Raka Off Licence in Clacton in London's East End, and who has learned an expensive lesson.

She got a phone call at 7.30pm from someone professing to be from PayPoint, someone who knew her name and knew her agent number. He said £400 too much had been taken from her account via her direct debit and telling her that in order to put it back it would have to be done straightaway (ie out of office hours), before midnight (before all the bank accounts automatically update) and adding that it could be done via her terminal.

She argued a bit but he managed to persuade her. He gave her a long number to punch in and she had to do it several times. When she cashed up a few hours later, she saw receipts for seven transactions worth £200 each = £1,400. They were all for pre-paid IDT (Mastercard) Finance. She dialled 999 but they couldn't send anyone all she got was a crime reference number.

When PP told her that she would have to pay and she said she couldn't, her terminal was suspended for four weeks until she paid up.

Since I seemed to be getting stories about bigger and bigger fraudulent practices involving PayPoint I asked spokesman Peter Brooker how many were there really? He replied: "We process more than 10 million transactions through our terminals every week and the number of frauds taking place would require more zeros after the decimal point than I can compute as a share of the total number of transactions. It may feel like more from the letters, emails and calls you receive, but they have to be put into perspective with the total volume of transactions."

He adds: "The issue with Mrs Patel is that she broke one of the most basic rules for having a PayPoint. We constantly remind retailers, and it is clearly spelled out in our training manual, that we do not call our retailers in or out of hours to ask them to put through dummy or actual transactions.

"As the nature of this call was so unusual and contrary to how direct debit refunds work, and Mrs Patel admits having her doubts, she should have put the phone down and called our contact centre, which is open from 7am-11pm."