I called Samsung guys few times about this problem and even the engineer couldn’t fix it, so i stumbled upon it’s technical manual on the triple Ws.
Here’s what helped in my case.

1.  Press Power Freeze and Fridge Temp. buttons for 8 seconds simultameously to get in the ready mode for a forced operation.
2. The display panel will return to normal after 20 seconds in the ready mode.
3.  At the ready mode, press any button(except Ice Type and Child Lock) once to start a pull-down operation, twice for a defrost cycle for the refrigerator, three times for a defrost cycle for the freezer and the refrigerator, and finally four times for cancellation of this function

Defrost  operation
1) At the pull-down mode, press any button again on the ready mode to begin the defrost cycle for the refrigerator.
 2) The beep sound continues for 3 second at the beginning, then ON for 3/4 seconds and OFF for 1/4 second until this mode cease.
 3) After this operation, the system will come back to normal operation.
4) At this mode, press any button again on the ready mode to operate the defrost cycles for both compartments.
5) The beep sound continues for 3 seconds at that time, then ON for 1/4 second and OFF for 3/4 seconds until the defrost operation cease.