I’ve updated my nameservers over 48 hours ago to CloudFlare nameservers but Cloudflare could not detect new nameservers. I checked my domain “sihami.com” in whois.net and nameserver correctly changed.
Your domain is in “clientHold” state.
While the nameservers are updated in the WHOIS, the domain itself is not delegated by the registry to your root zone (.com), and thus, your domain is not resolvable at all. Maybe it was also that way before you changed nameservers to Cloudflare.
Anyway, this is something that you should check with your registrar. Perhaps you have some warning on the domain in the registrar control panel. Maybe payment issues, stuff like that.
Once your domain is actually delegated via the .com registry, I’m pretty sure Cloudflare will see it.
$ dig @a.gtld-servers.net ns sihami.com ; <<>> DiG 9.13.5 <<>> @a.gtld-servers.net ns sihami.com ; (2 servers found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 20542 ;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1 ;; WARNING: recursion requested but not available ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;sihami.com. IN NS ;; AUTHORITY SECTION: com. 900 IN SOA a.gtld-servers.net. nstld.verisign-grs.com. 1549176420 1800 900 604800 86400 ;; Query time: 161 msec ;; SERVER: 2001:503:a83e::2:30#53(2001:503:a83e::2:30) ;; WHEN: Sun Feb 03 08:47:32 IST 2019 ;; MSG SIZE rcvd: 112