Sounds like you didn't use the correct amount of fermcap. 2-3 drops per gallon in primary is the recommended dose (at least on the bottles I've had, and read online).
I've used fermcap when I had more wort in primary than I was comfortable with (and not have blow-off). I've also had times where I thought I was safe, or forgot to use it, and had blow-off. Since moving to my new place I've fermented one batch, that didn't need fermcap at all. Of course, I was able to get the temperature of the wort to where it needed to be in order to have a calmer fermentation. The basement here is a nice temperature to ferment in. So far, I've seen it range from about 56-62F where I plan to ferment most of the time. I might shift to the finished area/room come the cold winter months, but we'll see there.