Westpac Bank is urging customers to question any unknown banking activity after a Tauranga couple believed they had wrongly been charged an overdraft fee.

Pyes Pa residents Sam and Casey Fredericks say they have been treated like 'idiots” since encountering what they believed was a glitch within their Westpac payment system.

Casey Fredericks with the ATM receipt showing $76 before the five day holding period lapsed.

The couple, who have four children, became suspicious last week when their debit visa balance increased from $76 to $525 before suddenly plummeting into overdraft.

Thinking a Work and Income New Zealand (WINZ) payment had been transferred into the wrong account, the couple used some of the money leaving the account with $219.

The next day they woke up to find the account $294 in overdraft.

Concerned with the statements, Casey initially rung Westpac's 0800 number explaining the situation only to be told the account statements had been updated and nowhere did it say the couple had $70 over the weekend instead of between $500-700.

'The customer service lady said ‘I'm not saying that you're lying I'm saying that it couldn't have happened', which really is the same thing I think.

'I was told to I had to go to the branch and talk to them. I was told a debit visa works like a normal visa and even if you don't have the funds in your account it will still take them out.”

However, Westpac external relations manager Chris Mirams says the transactions and debit banking system worked exactly as planned.

With any debit card purchase normal industry procedure is putting the transaction in a holding period of five days allowing the merchant to put the payment into process, says Chris.

'The merchant did not process the transaction until the five day old period finished. She [Casey] has then gone and clearly seen the money and not made any calls as to where that money has come from and spent it.

'The merchant has put the card process through, so the system worked exactly as the system should.”

Casey has since received a letter from her Westpac Chadwick Road branch manager outlining the procedure and why debits cards have a holding period along with a temporary two week overdraft.

'This is a timely reminder for customers to ask if they are not sure about any activity in their account,” says Chris.