I'am just new at this forum and want to ask (you physics minded) a simple question (certainly the question indicates a lack of understanding

How do black holes ever grow?
For is it not at the event horizon where time freezes (according to einsteins theory) for masses speeding up to the velocity of light? Clocktime at the horizon freezes relative to our clocks. Then, how can black holes ever accumulate mass in the timeperiods our clocks register? Growing implies that it occurs in our time.
Certainly there are black holes in the universe which must have accumulated mass in the lifespan of our universe. It has become clear that almost every galaxy contains a supersized black hole at its center.
Is this a real paradox? What is the fault in my reasoning?
The question bothers me already a long time!
MeMeX (the Netherlands)
PS: What a great website, what a great machine!