It sounds like you did everything you could. Let me help you with emailing your invoices with the correct header. 

We appreciate you for providing us with a screenshot to better isolate the issue. Did you create a new email template when sending emails? If so, it can be QuickBooks still uses your old template causing the incorrect name in the header. Here are two ways to apply your new template.

First, copy and paste the correct message before sending the email:

1. Go to the Edit menu and select Preferences.
2. Select the Send Forms menu and then the Company Preferences tab.
3. Highlight the template you want to use and select Edit.
4. Copy the message's body text.
5. Go to the File menu and select Send Forms.
6. Choose the email you want to send. Paste the copied text into the body section. Note: If you're using QuickBooks Desktop Enterprise, you select Edit Email first.
7. Press Send Now.

Lastly, reset your email later settings: 

1. Find and open the transaction you want to send.
2. Choose to uncheck Email Later box.
3. Press Save & Close.
4. Reopen the transaction. Select to check the Email Later box. Then click Save & Close.

This puts the transaction back in the email queue. It should now use your new default template. If you have performed the troubleshooting steps yet the issue persists, I recommend contacting our Technical Support Team. One of our experts has the necessary tools to check your account securely and perform a screen-sharing session to conduct further investigation into this behavior. Here's how you can get in touch with an agent:

1. In QuickBooks Desktop (QBDT), click Help.
2. Choose QuickBooks Desktop Help or press F1 on your keyboard. 
3. Click the Contact Us button in the Have a question? window.
4. Enter your concern in the description box and select Continue. 
5. Choose either Chat with us or Have us call you. 

Please take note of our business hours to ensure we can attend to your needs.

Additionally, I’m adding this resource where you can access our self-help articles: QuickBooks Desktop guide. These resources contain topics that will guide you on how to efficiently handle your taxes, payroll, account information, banking tasks, sales or expenses-related activities, and so on.

I'm always around to lend a hand if you need more help with managing your invoices or anything else related to QuickBooks.