Welcome to the Community, @meaganmkenney. QuickBooks Online uses browser cache to save files on your computer and may affect the loading performance when it gets full.
We can determine if the issue is caused by a browser issue by using an incognito or a private window. Here's how:
Launch Google Chrome as your main browser.
Then, press CTRL+ Shift + N.
Log in to your QuickBooks Online account and check to see if the Billing and Subscription page loads successfully.
If it does, go back to the main browser and clear its cache. It also helps improve the browser's performance.
Once you're done, restart your device for the changes to take effect. However, if you encounter the same issue, try using another supported, up-to-date browser.
For additional reference, read through this article: Cancel your QuickBooks Online subscription or trial. It also includes a link to cancel in case you purchased your subscription from iTunes or Google Play.