What does your contract with them state happens when they don't live up to the terms of the agreement? That's what this is. The agreement was that they would

What does your contract with them state happens when they don't live up to the terms of the agreement? That's what this is. The agreement was that they would provide a documented API and a well-constructed iOS app, and you would build an Android app, right? So now that they haven't provided at least one of those, that's a breach of contract. What does your contract say happens? Mine say if the scope of work changed by more than 10%, work stops and the contract needs to be renegotiated. If they don't meet their deadlines, work stops and the contract needs to be renegotiated. If something outside of my control occurs (users not showing up for feedback sessions or something) to the degree that it materially affects my work, work stops and the contract is renegotiated. Sometimes that renegotiation is just a couple of phone calls and an updated statement of work. Sometimes we kill the job and they pay their kill fee and we both walk away. What's your contract say?