“i still owed 400 towards the down payment. Owner ...

I assume based on the topic that includes "real estate" that the contract is for the purchase of land, and while I'm fairly comfortable in saying that any land contract must be in writing (statute of frauds), but I don't know all the facts, and I'm not clear about eighteen down payments?  You may find helpful resources by contacting the State's Attorney for your state, they usually have if you call them what is called a "duty attorney," in some states, who is responsible for taking telephone inquiries for that day, and they could direct you more specifically with a conversation that can fill in some of the details, and the bar association in your state as well should have a website with resources for non-lawyers, so calling them as well could get you more specific advice that addresses the particulars of this situation that aren't clear here.  If all else fails, there are usually numerous attorneys in the phone book who will provide free phone consultations.  I am curious as to who wrote the contract and did not include the down payment information and agreement, there are some general contract principles that may apply in this case (again, I do not know all the facts, and this answer should not be relied on as legal advice, I again would try the above three resources).  If the individual who is claiming that you are in breach (we aren't told why, but for the moment, again, I am just relating some general contract principles) drafted the contract and omitted the provision relating to the deposit, it is usually the case that any ambiguity in a contract is interpreted in the light most favorable to the individual who did not draft it; further, if the contract does not contain all the material terms, it may not rise to the level of a contract at all, since there would be no "meeting of the minds."  And we aren't told whether you were given receipts for the payments you made, or whether a separate contract was written that addressed the payment plan for this deposit, but it's always, always prudent for anyone paying anyone money for any reason, especially as a deposit, that they have a contract or some form of written acknowledgement of the agreement if in installments, or a receipt acknowledging the payment and what it relates to, because it's much easier to prove you made payments when you have receipts, and again, I am sorry we don't have more information, but I hope these general comments are helpful to you, it isn't clear why this person told you suddenly that there is a breach or why, but I wish you not only the best of luck in obtaining legal advice from one of the above resources on this matter, it is good to know that you recognize that simply because someone states something about a contract does not make it so, so you are clearly an intelligent person who will pursue this and get an answer from your state's legal community.  I do wish you much luck.