This is very unfortunate and I'm sorry for your experience. It is a very common tactic in places with extreme poverty. I've seen it (or rather been made aware of it) under various names in developing countries. For example, in Cote D'Ivoire they're called "les microbes." Always on the "things to be aware of" at embassy security briefs. The general advice from the guys who know best is if you find yourself targeted and can't get away, just let them have what they want (cell phone, wallet, etc.). It sucks, but it's the safest way to avoid serious injuries. The professional advice for avoiding this is usually go in groups, avoid areas where you're likely to be a target, be extra cautious at night.