What is the ruling on using a sum of money that was not withdrawn from the balance, knowing that it was withdrawn from a usurious bank, and is it permissible to give it as charity instead of returning it to the bank?

What you have asked about has two scenarios: 1. If the amount not withdrawn is the usurious interest: There is no sin upon you for not paying it to them; rather, it is obligatory, and this is a grace from Allah. 2. If the amount is the principal of the loan: It is not permissible for you not to return it to them; rather, it must be repaid. The fact that they are usurers or disbelievers does not permit taking their money unjustly.

We also remind that taking out a loan with interest is forbidden, and one must repent to Allah from it, due to the gravity of usury and its prohibition, which is known by necessity, and the severe warnings and prohibitions mentioned concerning it.