You didn't mention anything about what mildewcide you used when the house was clean. If you used just water, well, you didn't do much to clean the house (as you see).
When you use these chemicals, be sure to read the directions first before you buy to be sure you can safely, and properly, do the job. One thing's for sure. Believe it or not, you should be cleaning the home from the bottom up; not the top down when using a cleaner. Again read the can first, before you buy. My best to ya.