Website transitioned to Shopify, old hosting account closed. Users' browser cache remained. How long will it stay?

I had a website that was located on hosting. Now the company has transitioned to an e-commerce platform, closing ht eold hosting account. Now, any used who had previously visited the old website, will see the old landing page, but without any of the non-essential content (the see the banner, navigation, website structure, but following any links will show a JSON error message, and no images load).

Pressing Ctrl+F5 will show the new website, but next time I visit the website or just press F5, it loads the old page again. Going into the developer tools and deleting local storage makes the website show a blank page. Ctrl+F5 will show me the new website, but only until I press F5 again or visit the page anew. So there is something else that makes me see the old page. Furthermore, there is nothing about cache in .htaccess of the old website (I have a backup, so I can snoop around).

I understand I mihgt not be able to clear the cache on the users' side. How can I know how long the cache will stay on the users' computers, and whether it expires at all?