iPhone 5 screen is flickering randomly, the phone freezes and the screen turns black.

I bought an iPhone 5 in New York last December. Now I live in Bogotá, Colombia and I can't find an authorized service center because they said that only if I bought it from a local carrier they attend the warranty.

My iPhone 5 screen is flickering randomly, the phone freezes and the screen turns black… The only way to make it work is to reboot with Home and Lock buttons pressed at the same time. But in the process most of the times it flickers again, and again, and again. I couldn't find a reason to identify what could be causing the issue. Also sometimes when it freezes, some group applications get ungrouped, causing a big mess.

I already tried to restore the phone, remove the SIM, delete all applications with no luck.

Any sugestion? Thanks!