As others have said, if you are telephoned by someone who says they are from your bank, etc, DONT ring back immediately from the line they rang in on, they are able to somehow to keep your line open after you hung up from them, so that even if you ring a different genuine number, the scammer will be the person answering the phone!
A lovely and clever friend was defrauded out of £75,000.00 + which had come from her redundancy into her current bank account. A very competent sounding woman rang her to check her security details, the woman sounded so good and believable, that my friend changed her security details on the phone and lost all her money.
The bank says it is NOT responsible because of how the fraud or scam was done as this particular way is not yet covered by law. My friend has gone to the High Court to redress this, her husband is a solicitor so they knew how to relatively cheaply, and it seems likely she will get most of her money back, but immensely stressful. ?