It depends on what state you are in and what your state laws are.  I had a written contract at first then an oral agreement after that.  Oral agreements are upheld in Texas courts.  You just have to prove to the court that there was a change and why that change occurred - what agreement happened between the parties.  Because work is done by you in your state - your state law even takes precedence over particular parts of the contract - i.e., they can put anything they want in the contract but it doesn't mean it will be upheld - there is a provision in contracts that always states that - a clause put in every contract - I could put the wording here but I don't know if everyone would undrestand it so I won't.