Your mortgage loan is a contract; both parties are bound by its terms. Review the loan documents. If the loan allowed this rate increase, you are bound by it so long as the bank followed whatever requirements or procedures (if any) are set out in the document for the increase. If the loan did not allow this increase, or if the bank violated the procedure for the increase, then you could potentially go to court for a declaratory judgment (court determination) declaring that the higher rate  is not in effect, an injunction (court order) requiring the bank to charge you the lower rate, and/or monetary compensation (to recover any amounts you paid in excess interest).