Publicly freely available doesn’t necessarily mean that it’s legal for you to embed them in your website without some licensing agreement. (I’m assuming your site isn’t just a list of external links.) Just as a heads up.
Speak with a lawyer. There might be nothing, there might be something.
Are you sure the ISP blocked this on their own because you are competing, or did a rightsholder file a lawsuit and require the ISP to block this domain? Rightsholders are not required to send a DMCA takedown notice before filing a lawsuit
Can you ask someone who is their customer to do a naive call to their tech support, and complain that they are getting an error when trying to access the website?
Is the ISP blocking the domain, or is its DNS server returning nxdomain for it? I've seen ISPs provide modems which use the ISP's DNS as a default (via DHCP) unless configured otherwise. Try running `dig mydomain.com @1.1.1.1` to check if that returns the right IP.
Not sure what you can do if they're just serving whatever they want from their own DNS other than telling users how to specify another one. Maybe dnssec is relevant?
Can you market outside of the country, where the ISP doesn’t have reach? Surely the product you have is valuable if the ISP feels threatened by it.
Depending on how you built it, could you migrate it to a platform like AWS or Azure where the IPs you use are mixed up with other services?
Isn't that a clear case of tortious interference?
Are you hosting the service through their ISP, or some other hosting provider?
Buy other domain names and point them to your server.
Get a vanity IP address like 75.74.73.72. Make up signs telling people in your town to switch their DNS to Cloudfare or Google.
Looks like this is the authority of regulation in Albania
https://akep.al
Usually a telecom operator agrees to some specifications as part of winning the bid for the license. And usually those specifications include obligation to be neutral when transmitting data.
Try to find that spec, find the right section, and complain formally to the authority of regulation.