Can’t log into website – hacked?

Hi,
I am not sure, that it is correct to ask here. But now I’ll try.

I am being told that it is not safe to log into my website, because the SSL certificate is from *.fortinet.com. And that it can be because the website is hacked.

I made the SSL certificate through my webhost one.com.

And in the month up to this error message, I saw more and more traffic from US, which didn’t make any sense, as my webpage is in Danish.

Does anyone have a suggestion what to do?
Thank you very much!
Best regards
Henriette

The page I need help with: [log in to see the link]