Try this:

You have to get the captive portal page to display. Try these tricks first:

• Close all open tabs in your browser. If you have a secure site open ( https:// ), the portal can get confused. Close everything in your browser. If you have your startup setting “Continue where you left off”, then change it to “Open the new tab page” and open your browser again. If you don’t see the captive portal come up, try going to a http:// website as they can trigger the captive portal.
• If you are in a hotel you may need to log into the captive portal after a period of time to continue using the internet. This will force you to go through the whole thing again.

These are all temporary solutions and not the most convenient ones. You may want to raise a complaint to your ISP or if you are staying at a hotel you may want to bring it up to the management as this is an ISP issue.

And if you are using a VPN the only way to connect through a captive portal is to turn it off. Unless you are using Speedify bonding VPN.