Good post, I'm sorry to hear about your phone though. Sounds like those people have a pretty thought out plan and it wasn't the first time they'd done it.
When I was in London I only went for two days, and instead of buying an Oyster card I just bought two travelcards for each day, so you can just use it in the ticket barriers instead of putting money on an Oyster card. When it was dark I just used a taxi to get back even if it was pricier because otherwise I would have been walking by myself. (To anyone getting taxis, the back, inside, and front window (I think) shows their licensed taxi number. I wouldn't risk getting in a black cab without one unless it was a different taxi company.)
Also, I had a backpack with me, but I kept an eye on it. When you're waiting to cross a busy road and there is a large crowd of people, it's best to take it off your back and carry it in front of you because it would be easy for someone to take something out of it. If there are pockets on it, I would take valuable things out of them and store them elsewhere.