Ms Battell says scammers were "very cunning" at getting PINs out of people who made matters worse for themselves if they used one PIN for multiple cards.
Her office dealt with a case recently where a woman revealed a PIN that she used for more than one card.
The complainant took a phone call at work from someone saying she had won a $1000 gift voucher, and was asked for a four-digit password to redeem it. She gave three different passwords but each time was told it was taken. She was then given a random one.
"At the time she didn't know her handbag, with two Eftpos cards and a loyalty card for the retailer supposedly offering the voucher, had been stolen. The voucher was a trick to get her bank card PINs which she revealed to the caller," she said.
Ms Battell said the complainant lost $6000 because she revealed her PINs. She was tricked by a scammer who played on the fact most people limited the number of PINs they have.
"I know it's sometimes difficult to have a variety of numbers but we strongly advise people to have PIN numbers unique to each card you may have," she said.