Newbie : Change IP of NS to new IP failed

[Kadek Hendra Lesmana]

Hello everyone,

My company registered their NS a few years ago, and setted their NS as
Slave from their ISP's NS.
Few months ago we change public IP, so our NS IP changed too, say it
from <a.b.c.d> to <x.w.y.z> but the name is not changed
(ns1.myserver.com)
Since that no problem arised and I never check it.

Now we are setting our NS as Master NS everything's ok from our
intranet, but from outside (network-tools.com) we can't ping our NS's
domain.
ping ns1.myserver.com failed, ping <x.w.y.z> ok.
DNS check with network-tools.com shows ns1.myserver.com still refer to
old IP <a.b.c.d>.
The registrar only providing input of NS domain name not the IP
address, so I wasn't change anything.
Please tell me what should I do ?
Thanks in advance for any help.

Best Regards,
Kadek