Regarding the contract: I'm concered because in the US, a 17 year old can't enter into contracts. Thus, the contract both of you had is likely invalid unless 17 is an adult where you are. This can play to your advantage if you can prove this "man" was trying to take advantage of this "child". This will play to your disadvantage if you presented yourself as an adult (ie: lied) in order to get a contract. This point is moot if you live in a place where 17 is "old enough" to enter into a contract.

Doing what others have said and calmly and politely see if you can enter into a discussion with this person is the best way to go about it. You MUST put ALL anger aside and try to work with him.

However, if he still doesn't come through, then you can take legal measures. Again, your age is at a disadvantage for again in the US, you have to be an adult to sue (so maybe your parents could do it). However, to your advantage, most people cave in rather than going through a legal process so the mere THREAT of the suit may be enough.