But we don’t know why or by whom do the NS records not work anymore for our nameservers. Change them to the ones I listed, because they are also similar to them, but they are working.
VeriSign appears to have changed the nameservers from their end to ns1-2.epizy.com.namesilo.com. If you can get your registrar to set the nameservers back to their original values of ns1-2.epizy.com, your domain name will come back online.
This is not a configuration error on your side or on our side. VeriSign, the central authority of all .com domains, appears to have caused this issue.