NatWest reported that they were receiving up to 640 complaints a day in July and August.
Customers are often unaware that they have even authorised a payment and the money is being taken by payday loan middlemen.
It is thought the regulator, the Financial Conduct Authority (FCA), is now looking closely at such activities.
In the meantime, the Financial Ombudsman has repeated a warning that consumers should be vigilant.
It said it had received 11,500 complaints about “rip-off” loan brokers since April, more than double the number in the whole of last year.
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