How to disable internet connection on other computer?

Log into your router. Find his PC in the DHCP connected devices list. Grab the MAC address from that list and add it to the blocked list. He no longer has access to the internet.

Also make sure your own PC is password protected and the router is not the default password. If he uses wifi on another device, you will also want to change the wifi passwords.

If you can access the router, you may be able to block him.

do it in the router ban his mac address change the router password of course

Log into your wifi (I'm assuming you own the wifi, too), and block his machine by the Mac Address.  Look for the "connected devices" link.  Then make sure "Access Control" is turned on, then using Access Control, block his devices.  Named devices such as "Iphone" and "Unknown" may be more difficult if there is more than one, but usually computers show their name such as "Marv' Desktop PC" and the like.  You can disable each one until he pays the rent. 

Passwords: changing the password will only affect Wifi connections.  so, yeah, if he connects his phone, change the password. but this means you will have to log every device of YOURS in again, too.  Rather than doing that, ban his phone via the mac address too.