But when you cross the processing date, contact Congressman. There are only two senators per state while there are many congressmen. They have vested interest in you as you directly belong to their constituency. Senators have more cases to handle and less time for you. This was my personal experience. Others could differ but I respect that.
But contact Senators too. When I need help, I take from anyone willing to help me. It does not matter who he/she is as long as I get the end results.
But contacting Congressman/Senators does work.