What is the ruling on participating in auctions held by a usurious bank to sell properties mortgaged to it, and on purchasing properties through these auctions?

If houses are mortgaged to banks due to loans, it is permissible to purchase them from the banks and participate in the public auction if the sale is due to non-payment of the principal amount of the debt. However, if the debtor has paid the principal amount of the debt and only the usurious interest remains, then it is not permissible to sell the mortgaged property, because the interest is void, and it is not permissible to purchase it from the banks because it is being sold unjustly. It is permissible to collect auction fees from the price of the house.