Hi, vinvalentino. It sounds like there may be a lot of things going on in your install that may be causing problems for each other.
Here are a few questions so I can get a clearer picture of what you’re working with:
1. Which revised tickets.php code are you using? Do you have a link to the thread where it was specified?
2. Did the availability work correctly before you changed the tickets.php?
3. If you have other WooCommerce add-ons installed, it’s possible that there could be a conflict with one or more of them. Have you tried disabling all other plugins expect for TEC, WooCommerce Tickets, and WooCommerce?
Hopefully, with these answered, we can get you pointed in the right direction on how to resolve this.