How to stop unwanted Safari Notifications?

I have looked at a website a handful of times in my life and somehow, have started receiving safari notifications pop up for new forum posts. I must have had to set up an account at some point so I deleted that on the site, I've checked safari and notification settings, all set to OFF, and yet I still keep getting these notifications. Any ideas where else can I find it?!

I would never have given the site permission to bombard me with irrelevant content but it must have been something that kicked in last time I looked at the site. I've also tried clicking on the notification which just takes me to the site, which I have no account for so can't change any settings?!

It's driving me nuts.

[Re-Titled by Moderator]