This is just one of many telephone numbers to get through to NatWest bank customer services.
As a NatWest customer, I have used this number many times. It is safe to use/connect to.
My experience is they are a Fraud activist bunch using this number and accessing your bank account / details and pretending to be the bank informing you of fraudulent activity on your bank account when it is actually them doing the fraud!!!
Bank should know better and remove their name that is attached to this number