If you don’t recognise a transaction on your account then you must notify us a soon as possible. That could be an deposit into your account or a withdrawal that you don’t remember making. There may be error, fraud or a genuine transaction. If you can contact us then we will investigate for you. If the transaction is on your Engage Account, then contact Engage to investigate engageaccount.com.
And no, if some money is paid into your account in error, you cannot keep it. That could be theft, so do please let us know as soon as you can and we will correct the error. This article explains why can-you-keep-money-accidentally-paid-into-your-bank-account?