I can't access a particular website on my mac
I've just started using my mac after several months out of the country. I'm trying to access a regular client's website address but it comes up with 'The Site Can't Be Reached'. I've tried opening it up on other devices and the website is fine. I've tried using Chrome, Safari, Firefox and also uninstalled Mac Keeper. . I've restarted by mac and the router several times. I'm operating on macOS High Sierra version 10.13.1. I'm not sure what could have changed during my absence to cause this. Any suggestions?
iMac, iOS 11.3.1