Santander customers hit by the bank's latest service blunder have been reassured any bogus charges will be refunded.

The Spanish giant hit numerous credit card holders with a £12 late fee this month despite many victims insisting they have made payments on time (see the 0% Credit Cards guide).

The bank, which topped our worst customer service poll in August and again this month, won't confirm how many customers have been wrongly charged, only stating the glitch affects "a small number".

Many MoneySavers who hold an Asda credit card, issued by Santander, have complained on our forum of incurring these spurious fees.

One user, starM, says: "I checked my statement and a £12 late payment charge has been added. The payment was taken by direct debit so there is no reason for a late payment charge."

It is unclear how many of Santander's products are affected as, when asked by, it only stated those with Santander-branded and Asda-branded cards may have been hit.

The bank did not confirm or deny if customers who hold other cards it runs have been charged (eg, Debenhams store card users).

Refunds promised

Santander stresses it started writing to customers as soon as the problem was uncovered and all charges will be refunded automatically, so no action is required.

Nevertheless, if you've been hit, closely examine your next statement to ensure the refund has been made.

In addition, Santander promises that where a customer was wrongly charged and it then alerted a credit reference agency of the 'late payment', the bank will rectify this error by removing the red flag from their file (see the Credit Rating guide).

A Santander spokeswoman says: "We can confirm a small number of customer statements were affected by a technical issue. This was immediately rectified and we have written to all affected customers to apologise."

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