Generally speaking, when you enter in to a contract the terms of the contract are binding on the parties.  In other words, you need to read the agreement and see if in fact it addresses the issue that you have raised here and if it does what it says about resolution.  If it does not address the issue then the general principles of contract law as codified in your state will apply.  Again, in general, if parties do not live up to their end of the contract it can be viewed as void or voidable under the law (these are different concepts and have different outcomes).  The law does not expect you to have to wait indefinitely for the car while maintaining a financial obligation.  Seek legal help and seek to cancel the contract if that is what you want.  But the contract should speak to at least how cancellation should be made (in writing, I am sure).  Good luck.