I'm Miles from the Social Care team at Shopify. I will be happy to help you fix this issue.
When you are navigating to your product, are you doing so via a link in your menu or navigation? If so, the issue might be that the old product is still linked to the menu, and you may need to update the link. To do this, you can follow these steps:
Check out our guide on adding, removing, or editing menu items for more help.
If this isn't the issue, check that your product is active in your Online Store. By default, new products are created as a draft, so it may be that your new product is still not active. To check which products are listed as a draft and change them to active, simply do the following:
To learn more about this, you can view our guide on adding and updating products.
Without links and screenshots, the suggestions above are based on hypotheticals. If the above options don't resolve your issues, please reply to this thread with links, screenshots and a detailed explanation of the issue and I'll be able to have a better idea of what the issue may be.