Hi there Aya,
Thanks for getting in touch with us and sorry to hear about this issue. Let me help you out …
1. I unchecked the woocommerce check complete automatically option. Is this enough to be sure this glitch is gone? putting in mind we are already live so such a mistake can cost me my job!
Please start by checking out this article on the WooCommerce specific options for tickets → WooCommerce-Specific Ticket Settings. I recommend creating a test event and testing the workflow once everything is configured. Additionally I strongly suggest you set up a staging / development site so you can test the site functionality before making it live!
2. Can you please tell me where can I find the tickets already sent to check them out manually? On my email they do not appear in the sent box.
Generated tickets can be found in the attendees report for the events → Tickets: Managing Your Orders and Attendees.
3. Deleting the customers from attendees is enough to cancel the ticket and redeem it useless??
Check this article out → How to Refund or Cancel a Tickets Order.
Please let me know if you still have any doubts,
Best,
Nico