What is the ruling on dealing with the FATEN Lending Institution, which requires paying a bank commission to the bank as an intermediary for purchasing a computer in installments, knowing that it claims to deal with an Islamic bank, while the bank is usurious, and they cite your fatwa no. 173087?

There is a difference between the Sharia (definition)-compliant dealings with the "Fatin" institution and its usurious dealings with banks. The fact that the latter is forbidden does not mean that the former is unlawful. It is permissible to deal with mixed companies whose primary activity is permissible, even if they deal with usurious banks. However, it is not permissible to engage in murabaha with this institution if its financing involves usurious interest that you pay, as this constitutes cooperation in sin. It is permissible for the company to stipulate a guarantor for the payment of overdue installments, provided that the guarantor does not take a fee for the guarantee. As for the mentioned bank commission, its ruling depends on its purpose.