Genuine number for a department that unfortunately isn't part of the main banking system. Branch are clueless about them but if you call their banking number and as a colleague to ring the number, they will verify that way
Received letter for mortgage fee refund. This seemed to fit with actual details. Called the number and they tried to get me to send a signature with proof of addresses before they sent a cheque out. All seemed a bit off so phoned Halifax who confirmed likely a scam