Is that legal to push to sell something which is no longer yours?

Even though the original lender is no longer the holder of the promissory note, it may still be the loan servicing agent who has authority to conduct the foreclosure. Or the current holder may have appointed the original lender as its trustee to conduct the foreclosure. Otherwise, if the foreclosing bank does not have legal authority to foreclose, you can raise that fact in opposition to the motion. You would have to file a legal brief and declaration in the court. You will need assistance from an attorney, or at least a paralegal, to help you do this.