What kind of response would you get if you said "Thank you for your continued interest in my home daycare but since you didn't come the last time we set up a visit I see no sense in setting a new time. If your needs change please let me know."
It is blunt, gets your annoyance out there but ends with saying something to the effect of if you get your act together and think you can be a responsible parent for once we can talk. Where it goes after that is well up to you.