I'll let Krydos take a look at this as I don't see anything wrong on our end. Zone files look fine, check fine, and resolve when queried directly. He's the expert on these name servers though.
I did correct missing A records for your subdomains on Cody (my fault as when I restored this for you I didn't know the DNS servers don't actually talk to each other...), but that didn't resolve the fact the root domain itself still won't resolve.
As for this morning (on a different computer), I get this. The major DNS providers just return nothing at all for your domain. At work last week they returned an NXDOMAIN.
C:\Users\Owner>nslookup sgnetworks.in.eu.org ns1.heliohost.org
Server: UnKnown
Address: 2001:470:1:1ee::3
Name: sgnetworks.in.eu.org
Address: 65.19.141.67
C:\Users\Owner>nslookup sgnetworks.in.eu.org ns2.heliohost.org
Server: UnKnown
Address: 2001:470:1:1ee::2
Name: sgnetworks.in.eu.org
Address: 65.19.141.67
C:\Users\Owner>nslookup sgnetworks.in.eu.org 1.1.1.1
Server: one.one.one.one
Address: 1.1.1.1
Name: sgnetworks.in.eu.org
C:\Users\Owner>nslookup sgnetworks.in.eu.org 8.8.8.8
Server: dns.google
Address: 8.8.8.8
Name: sgnetworks.in.eu.org