Caller: They said they were from visa

An american accented lady called to say there had been some suspicious activity on your visa card - it went like "are you Miss _____" I said yes - she them repeated there was some suspicious activity on your visa card - I asked what visa card - she repeated again there was some suspicious activity on your visa card - and again I asked what visa card - she said National Australia - I said I do not have a NAB card and she hung up.