In such cases, the first thing which you should check is whether you are using the correct DNS records for your domain or not. To know how to check DNS records read the article How to find DNS records?
There are many registrars all over the world with different TLD’s referring to a specific region/country. There are few registrars which have a specific requirement when it comes to DNS servers OR Name servers. For example .de, .br, .com.br, etc. At times, our DNS are rejected as the requirement of these registrars is not met.
If this is the case for domains hosted with us, contact our support team. Check the exact requirement of domain registrar & pass on the detailed information to our support team. They will find a solution OR alternative for this issue.