I have also had the “hi mum” text, with phone supposedly knocked into the sink. I contacted both my kids on their mobiles to see if it was them, and it wasn’t, so deleted the message without responding. You don’t want them to know you are a real person, so don’t reply. It’s sad, but you can’t take any of these things at face value. The number of times I have been supposedly being investigated for tax fraud! If they don’t address you by name, though, that is a real giveaway.
My DH was once phoned by his bank to ask about the quality of their service and he refused to answer their security questions as it was them that had called him, rather than the other way around, and then went to the bank and found out it was genuine, but the cashier agreed he had done the right thing. It’s a problem, though, with so many bank branches having closed down that it is no longer a simple matter of popping down to the branch to speak to someone if you have a query.