My guess: You didn't have 6:30 on your clock.
Why was my game ended
Let me guess.
You havent done a single move for half of the total available time ( 15min/2 = 7.5 min ).
Chess.com have an anti AFK system that prevents people to waste other's time by forcing people to wait 1 hour on a winned game. Happens a lot of times that the loser dont want to resign and want take a revenge just making waste other's time ( leaving window open just to let the time pass).
Next time remember that you have to do move in half of the total available time.
It said I lost on time but I still had 6:30 on my clock in a 15/10 game. I wasn't disconnected. I was in a tough positin and was thinking for a long time but that's why I was playing a 15/10, so I would have time to think about a tough position if it came up.