Better look at this as a lesson learnt that.
1. 50 minute connections are just tight. Better be safe with at least two hours (or longer, for your own peace of mind)
2. Don't put anything you can't afford to lose in your checked luggage.
3. The moment you realize your connection is in danger, start googling alternative flights before departure. You could have asked to be rerouted via the late departure flights to MXP/FCO/BCN/LHR. You might have had a chance!

4. Be aware of your situation and get clear answers from agents. The agents in Singapore who told you it will be dealt on the plane are the ones who fooled you. No way you'd make a 50 minute connection after a 65 minute delay! Nothing would be done in the plane.