Yeah you're right many people got stuck on the coin puzzle, that's my fault :'(
About the solution for room number 13, it might really not make a lot of sense but I wanted to fit the loop theme a little more, so when you call room number 1 you get the first phone dialogue of the game ("it seems you're stuck in a loop, etc"), but this time it is YOU who says it, implying YOU were Number 13 all along! Not necessarily a loop but it does connect to the start of the game.
Thanks a lot for playing, and for your input!!