What should I do if one of the providers blocks access to our site for their subscribers?

Question

Domain Name System

Or does not block, but simply has technical problems when opening our site (for example, DNS problems). For all other providers in the world, the site opens properly.
The site is not included in any black lists, it does not contain prohibited materials, and it does not violate the laws of any country. The problems of discovery are purely technical. When subscribers contact their provider's technical support, the issue is resolved, but 99% of users think that we have problems.

Answer 1

Change hosting and DNS as a result...

Answer 2

There could be a lot of reasons. It can be a tricky nat, problems with IP connectivity before hosting, a cant with DNS (your hoster or provider). The most correct thing is to ask the provider, or rather, his shift. You can play jokes yourself by checking pings, DNSs, traces, but you need to be connected to the operator's network.
Well, if you want for sure, as advised above, change the host. Or, as an option, buy a cheap hosting, attach a reverse proxy to it and ask the provider to register your domain to this proxy in your DNS.