"Din Don, Din Don, intervengo da Cesena, ma nessuno ha fatto gol"
It means: "Ding Dong, Ding dong, I'm speaking/calling from Cesena, but noone scored a goal"
They are making fun of that Milan commentator and the Milan fans who were given a wrong info that Cesena equalized against Juve and they started celebrating like mad, even though Cesena never actually scored a goal and we won 1:0.