Contact the President: https://www.whitehouse.gov/contact

The Congressional Switchboard Number is 202-224-3121. 

Contact your Senators: https://www.senate.gov/senators/contact/

Contact your House of Representatives: http://www.house.gov/representatives/

Here are some articles about how to make calls to Congress and why you should:

Here’s Why You Should Call Not E-mail Your Legislators

How to Effectively Lobby Your Congressperson

A political insider’s viral advice on how to make your Congress member listen

Contact your State Legislators: https://www.congress.gov/state-legislature-websites