What is the ruling on keeping surplus money in a bank account after canceling all banking transactions and withdrawing the principal, knowing that the salary is transferred to this account and cannot be canceled?

If the questioner is certain that the amount is not rightfully theirs and was returned to their account by mistake, then it is not permissible for them to own it or dispose of it. It is not permissible to deal with usurious banks, open an account with them, or transfer salaries to them, except out of necessity and in the absence of an alternative. It is not permissible for the questioner to benefit from the usurious interest earnings to pay bank fees or other expenses; rather, they must dispose of them in their prescribed charitable channels and pay the fees from their principal capital.