The gravitational pull from a black hole is so immense not even light can escape. Light is indeed the fastest thing we know of but it is still affected by gravitation fields. The force of a black hole literally pulls light into its centre so that we do not see it.
At the moment I don’t think we actually know the shape of a black hole as we cannot see them (as they suck in all the light around them). It is possible it could be a sphere, doughnut or cylinder shape, but the chances of it being flat are very slim.