Yesterday, 8pm cet my internet suddenly dropped to 0.2 mbps. I have made an nmap scan of the network and found several ports open including port 20005 which i find suspicious, because internet says its a port often used by trojans and viruses. I would like to close that port on the router. But how can i do that? I cannot find the setting for this. Please help. 

ps: i dont know the hardware version so i just put v3 there