Unlock my locked Macbook

Hi. I’m currently in Japan for a short student exchange program. Yesterday, my Macbook pro model A1502, got locked for unknown reason. First it asked for a 6-digit PIN, not knowing what the problem was, i punched in any 6-digit that i can think of. Then I restarted my computer and it just show a padlock and a box for the password. I looked up online on how to unlock it and the best solution would be to make a trip down at the Apple Store. However, they’ll need to see a proof of purchase or ownership which i don’t have it with me. Obviously didn’t see it coming 3 months ago when i was packing. Can someone please help me? What should I do now?