Help - bank scam

This is a complaint about Nat West who I have been a customer with for over 40 years.

I was subject to a scam which was perpetrated on me on the 17th December 2018. It resulted in us (myself, my wife and my daughter) having £15,690 removed from our bank accounts and has left us completely devastated.

I consider myself savvy, but this was extremely professional. I was persuaded to give out my mobile app number on the basis that this was an activation code and the mobile app needed to be urgently deactivated. When I challenged this saying I never give out a code, I was told the bank would never ask for a PIN code, but they needed the activation code, and this was different.

Again, I challenged the caller asking to confirm they were from Nat West. They told me to look at the number they were calling from to check it matched the enquiries number on my debit card. I did and indeed it did match.

I think there is a vulnerability in the NatWest security system which allows a single number to access the mobile app. As I had not used it for 2 or 3 years I was persuaded that the number I was giving out was an activation code rather than a PIN number. Had I been using it regularly I don't think I would have done that. Surely there ought to be a system that if a feature is not used for certain period it is all automatically deactivated?

The caller then rang the following day at a pre-arranged time and clearly had made some transfers between our accounts already. He had cleared my wife's and my daughter’s account and my overdraft. He went through about 20 direct debits with me, ostensibly to check I wanted them all transferred to the new account – in hindsight this was a further confidence boosting measure. Using the card reader, I was persuaded to transfer the sum of £15,690 into the account which I was assured was my new ‘safe’ account. It was set up with my name and reference.

Still thinking this was genuine but feeling a little uneasy, I called NatWest fraud line who said it was likely to be a scam. They have since said the beneficiaries account had been cleared and no monies could be recovered, the bank had no liability. I received a highly impersonal standard photocopied letter from Nat West. In my view displaying a complete lack of concern for a customer of over 40 years.

Aside from the systems vulnerability of the single access code for the mobile app, the second issue I have is that the perpetrator was able to move amounts from accounts which are linked but not related to mine, although were accessible through the internet banking site, and by doing so was able to take money out of my wife's and daughters accounts. without any action on my part. This also seems to be a vulnerability in the internet portal.

The police have identified a suspect and they tell me there is a chance they might be able to pursue charges.

Do I have any comeback against Nat West or other suggestions on what I might be able to do to recover any funds?