What is the ruling on mortgaging a house to the bank to buy undeveloped land for cultivation and work, knowing that one works for a company that deals with usurious banks and that all banks are usurious?

It is not permissible to deal with usurious banks except out of extreme necessity, provided that there is no Islamic bank that fulfills the purpose, and that the transaction is Islamically permissible. If the intended transaction is for the mortgagor (the homeowner) to take out an interest-bearing loan from the bank, then this is forbidden and impermissible.