I got in touch with our Systems team and the IP address that the server your website is hosted on is using is included in a list of addresses with a bad reputation. Our firewall automatically stops all the IP addresses included in this list.
You can check that here: hidden link
I asked if there's any way we can unblock that IP but this list is kept by Amazon and used by thousands of sites all around the world so we don't have access to it so we can't unblock it.
You would have to use a different hosting service I'm afraid.
I hope that you will find the information above helpful.