What is the ruling on the housing allowance remaining in the salary despite moving to government housing, and informing the employer repeatedly without result, and is this money considered unlawful?

The mentioned amount is not yours, and it is not permissible to take it or benefit from it. The error of the official does not make it permissible for you to do so. The officials should be alerted to avoid the mistake. Furthermore, the amounts that were deposited into your account must be returned to the responsible party, unless the authorized person grants you permission to benefit from them. And know that "whoever gives up something for the sake of Allah, Allah will compensate him with something better," and "Whoever fears Allah – He will make for him a way out And will provide for him from where he does not expect."