To the first point, the amount outstanding may be too large for small claims court in your jurisdiction. If that's the case, you could be looking at a more drawn-out process for resolving this in your local courts. Consider speaking to a collections agent or collections attorney about how to handle it. You'll lose about 1/3 of the money in their contingency fee, but you'll be able to get this off your plate and get back to business.
For the future, give some thought to having a written contract, and to making your non-payment policies clear. You shouldn't have to keep performing cleaning services if you're not getting paid. A local attorney can help you figure out how best to do that.