Frank,
I can help you out with this.
That line is put there by your theme or WooCommerce. The best thing to do is use a Developer Tool in a browser to find css that is causing it.
https://developer.chrome.com/devtools
Then you can add some custom css to remove the line.
I am unable to tell myself without seeing the site, I do know it is not put there by the Events Calendar WooCommerce Tickets.
If you can provide a link to the page I can take a look and make a better suggestion.
Please let me know.
Thanks