Can u explain me how a player still playing while his time is over?

Here is the link lichess.org/zKQ9BSzq
Ps i have lost 12 points in this game because of this bug

What would you do with those 12 points?

He premoved the last few moves. See the "move times" tab below the board.

You were white in the game.
You had 1.3 seconds on the clock at the end.
Black was out of time. black won the game due to timeout !!!
You should have won the game.
this is a clear bug in the software. too bad.