Hi there, @Lindajp747.

Let's perform some troubleshooting steps to get this fixed and get you back to working order.

To check if it's a data issue, let run the Verify and Rebuild Utility tool. It's a good start when it comes to fixing data-related issues.

To run the Verify Data utility:  

1. Click the File menu.
2. Select Utilities. 
3. Click Verify Data. 
4. If there are issues found, you’ll be prompted to Rebuild Now. 

Here’s how to run the Rebuild utility:  

1. Click the File menu. 
2. Select Utilities. 
3. Choose Rebuild Data. 
4. Click Ok on Rebuild has completed.

After verifying and rebuilding the data, go back and try to use the customized invoice template again to double-check.

For additional troubleshooting steps, please refer to this article: Resolve Data Damage on your Company File.

If the invoice still won't follow the customized template, I'd suggest copying the template and delete the original one. Here's how:

1. Go to the List menu, then select Templates.
2. In the Templates window, select the invoice template.
3. Select Duplicate from the Templates drop-down.
4. Choose Invoice, then click OK.
5. Once done, right-click the original template and select Delete.

You might want to check out this article to learn more about the customized templates: Use and customize form templates.

Please let me know if there's anything else I can help with and I'll be back in touch.