Purchased an Ipad Pro 11 inch Gen 6 but received a 4th Gen

As we are all other end users, we can only offer suggestions. Apple won't see your concern here.

Which online Apple Store? The U.S.? Another country/region?

We don't know how you determined the model, so let's start from the top. Please do Settings > General > About and tell us the what that shows for Model Name and Model Number. If Model Number starts with "F", it is a factory refurbished unit.

Now tap the "Model Number" line. It will change to "A" followed by four digits, Tell us that code.

For security reasons, please DO NOT post a serial number.

However, you can securely enter your serial number into this Apple page to see what Apple shows:

Check Your Service and Support Coverage - Apple Support

Thanks. That indeed returns to a iPad Pro 11-inch (4th generation) (Wi-Fi). Did you order of the Apple refrub page?

Did the serial number on the invoice match the one on the iPad? If you did not save the invoice and, as the tablet was bought recently, you should still be able get the invoice from your Apple Account > Devices page.

As we are other end users, I doubt anyone here can recommend actions beyond what has been offered. There is an Apple Corporate presence in Cork that may be more effective than Support in resolving this unusual issue:

I'm afraid, contacting the official Apple Online Store is the only option for you:

Contact - How to Contact Us - Apple

Or can you visit an Apple Store next to your place?

Apple - Find Locations