I have set up the parental controls, which originally worked very well. My son has changed settings on his local computer and can now get in when he feels like it. I have tried binding IP with mac address etc, but nothing seems to work.
Welcome to TPG Community!
We don't have any control on the settings that your son has done with his computer, but it is possible that he installed a VPN to bypass the parental control of your modem/router.
You may check other forums or search for any information on "how to bypass parental control" as it will give you some idea on what was changed with the device.