@pierre789 

What is the led status of the Archer VR300? 

If the internet led shows off, please login to the web UI of the Archer VR300 and show me a picture of the advanced-status page.

To do a comparison analysis, please hard reset the VR300 by holding the reset hole for 10s with it powered on. 

Then connect your computer to the Archer VR300 by wired cable and try to setup the broadband connection with the username and password given by ISP. Instruction attached below.

https://www.tp-link.com/support/faq/921/

If the computer works fine, please connect it back to the Archer VR300 and clone the MAC address under advanced-network-internet page,

If the computer does not work either, I'm afraid that there may have some special settings at ISP's end, like mac filtering or mac binding which makes specific router can get internet with the same username and password. You can give them a call to fix it. 

May it help. 

@pierre789 

Have you ever tried to hard reset it and connect the laptop to the VR300 by wired cable to setup the broadband connection? 

If the laptop works well, you can login to the web UI of VR300 and clone its mac address.

Otherwise, you can contact the retailer to get a replacement and then test whether it works fine.

Best regards.