You need to find the email you got from Ebay when you paid.
From that email, what is the latest estimated delivery date?
Sellers don't always respond to messages or even add tracking to show items have been despatched.
If you have not received your item by one day after the latest estimated delivery date from the Ebay email, you can open a case through Ebay stating your item has not been received.
Don't message the seller to chase delivery or non-receipt. Open a proper case.
Report that your item hasn't arrived
You have up to 30 calendar days after the estimated delivery date has passed to report that an item hasn't arrived.
The seller should respond within 3 business days to provide a delivery update, offer a replacement, or give you a refund. If you're getting a refund, it will go back to your original payment method. Refunds are typically available within 3-5 business days.
Report an item you didn't receive
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)