Absolutely frustrated and still missing one item.

Placed an order online on 18/11/25. One item was short delivered. Since then, I have sent a minimum of 20 emails, and made calls every day, sometimes twice a day since the 20th. Today I was told that all the cases/queried on my order query were closed - wasted 20 minutes while the agent opened a new complaint/case. To add insult to injury, they have sent me 3 different invoices for the same missing item! I am so frustrated I could do physical harm at this point.