Transport damage through the mail!!

Hello, last one got a broken subwoofer delivered by the post office. The package was insured…. Did not notice this until 3days later…today… How do I have to proceed now to get compensation for the woofer? Subwoofer costs new approx. 200€…..is used…have paid 80€…is not to buy anymore, since already about 4years old… Mfg Olaf