Alec here, just thought I would introduce myself, as I am from Bega.
I had some joy growing capsicum when I was in Sydney. I never had the problem you describe. Too much water? Early rotting is usually a sign of overwatering? But black spot sounds like a bug of some kind. Got a pic?
Jen here, from Gold Coast Qld
Did you add Dolomite lime to your soil before planting your capsicums? Its add calcuim to the soil to stop bottom end rot in tomatoes, capsicum, egg plants - same plant family.