I went to Paris to recover from the grief of losing my dog.

All was going well until I took a taxi from a rank outside Musée d’Orsay to my hotel near Notre Dame – a 12-minute journey.

The meter showed €9.70 (£8) and the driver asked me to get out of the cab and pay on the card reader through the car window as the internet connection was poor. While I was doing that he surreptitiously altered the amount on the screen, and when I returned to my hotel I realised he had charged me €570.

I immediately filed a fraud report with my bank, Monzo. It rejected my claim because I have no evidence of the agreed price.

This a common scam as far as I can tell, and it relies on the fact that you don’t pre-agree a price with a cab driver, or get an invoice or receipt.

This will keep happening to people unless banks start clawing the money from the scammers.

RG, London

This is a similar scam to the case of the £600 slice of cheese in Brazil, which I reported last month. Whether it’s cheese or taxis and wherever you are in the world, con artists take advantage of tourists’ unfamiliarity with local currency and furtively adjust the price on the card reader in between the customer approving the sum and presenting their card.

Because it is a face-to-face card transaction, it does not qualify for the protections offered to victims who are tricked into paying fraudsters by bank transfer, a scam known as authorised push payment fraud.

The voluntary chargeback schemes offered by debit card issuers, which allow a disputed payment to a merchant to be reversed, tend not to work in these cases because there is no invoice, or receipt, to prove the price was inflated.

However, Mastercard, which is what you paid with, has recently changed its chargeback rules for disputed amounts, and a bank statement on its own will now suffice unless the vendor produces evidence that the correct sum was charged.

I pointed out Mastercard’s new rules to Monzo but it refused to budge. “We’re confident in our decision not to raise a chargeback because we believe it wouldn’t have been successful without the supporting evidence required,” it says. “We urge customers to always double-check the amount before making a payment.”

I disagree with its reasoning. The driver would have to support a challenge with evidence that the fare was correct. You could therefore escalate your case to the Financial Ombudsman Service, citing Mastercard’s new rules.

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