How sould I do that I can not find out where send the court pape

According on Law of California .Any out of state business in california has to have agent in the state.I am going to sue CitiBank( S.Dakota)N.A.But could not find their agent in CA .I consulted with court advisor and sent a few times court file to different place (include Sec. of state --state govement ).All return it back to me .What sould I do ? please point it out .