On the last run after the prong was set @ 80 m +/-; The slickline supervisor started POOH, and reduced the speed once close to surface. At 4 m below the rotary table, the slickline supervisor kept POOH while trying to reach the Assistant Operator via Walkie Talkie to give him signals to stop, meanwhile the tool string went out of the landing joint and hit the upper sheave causing the slickline wire to be parted and the tool string fell on the Rig Floor.