When a browser stored a lot of caches, it could cause problems like latency issues. As an initial step, you can press the F5 key on your keyboard to refresh the page.
If you're still getting the same result, we can do some of the basic troubleshooting steps. You can use these shortcut keys depending on the browser you're using:
Google Chrome: Press CTRL + Shift + N.
Safari: Press Command + Shift + N.
Mozilla Firefox: Press CTRL + Shift + P.
Once signed in, go back to your billing and subscription page and update your card from there. If it rectifies the issue, go back to your main portal and clear its cache to remove the browser's history or you can press CTRL+Shift and Delete key on your keyboard altogether. You may also try accessing your account using another supported browser.
You can get more details about changing your credit card info in the following articles below: