I have been using QB for 3 years, never had these problems.1. When I send out invoices, they end up by different clients?

Welcome to the Community, Karen. 
 

First, make sure the customer’s email address setup in the invoice is correct. If so, let's troubleshoot your web browser to identify what's causing this issue. 

Here's how:

1. Relaunch your browser.
2. Open your QBO account using a private window.
3. Delete your browser's cache.
4. Add Intuit as a trusted site

Additionally, for a smoother way to record sales transactions from your customer, check out this guide: Record invoice payments in QuickBooks Online.

If you have additional questions or clarifications about the invoice setup, please include them in the comments below. We're always here to help you.