@hidalgo22 I presume the cable is connection between modem LAN port and the router WAN port. Remove the cable from the modem and see if you can regain an access to the router. Make the screenshots,...

What modem are you using ? Post a screenshots of the router WAN and LAN settings here.

@PinkyS Upgrade the router FW to the latest one from here. Can you post these sceenshots: Who is your ISP, do you have a direct cable to C20 or it is connected to an ISP modem/router ? Are you aware...

@hidalgo22 Do you have more than one tp-link device in your network ? Try connect to the router directly via wi-fi (details for SSID/wireless password - sticker on the bottom of the device). Then...

If your device is still under warranty then contact the retailer for help. If he can't help then contact your local support for a resolution.

@GA_Polo OK, so after all the correct public IP address is updated into the no-ip database. Can you move the C6 web management port from the default port 80 to something else (8080 for example) and...