This might happen as a result of your DO/AWS server IP address being banned in the location you are checking by the ISP.
To test this, try opening your domain using a proxy/VPN service for another location. If your domain opens using your proxy/VPN you’ll need to change the server of the domain.
To do so, just follow these steps:
Create a new server in Zeustrack on the Websites > Servers section and press the New Server button to create a new server in a region other than one banned in your location.
After the server is initialized, take its IP address and set it up in the A-record of the DNS domain settings found on the domain registrar site. To learn more about these settings CAREFULLY check these docs:
The Overview of How DNS Works
Zeustrack approach to set up a domain and problem-solving
Go to the domain settings Websites > Domains section and click the Edit button to edit the domain. Select the newly created server from step 1 for this domain.
Wait for the DNS to update. DNS update time depends on the TTL settings of the domain set by domain registrar (find out the TTL time from the registrar settings or from support)
After the DNS is updated and the domain status is Online, check the domain availability again by opening your domain from your targeted geo.
So what about the server you’ve already created? Just use it for another location where the IP won’t be banned. Going forward, it’s a good idea to use an online-checking tool such as this one, to avoid the problem in the future.