can't get ride of www.playamo.com notifications - help please

Hi there !

I've started receiving push notifications on my Mac from a website called www.playamo.com - apparently, a gambling website - which I've never signed up for.
I've tried deleting it from 'Notifications' (found on 'Settings') to no avail - I keep getting those notifications.
How do I get rid of this ?

I'm running Mac Os Mojave 10.14 on a 13' 2015 Retina Macbook Pro (2.9Ghz i5, 8gb ram)

Thank you so much !