Ask HN: Has my domain name been hijacked

A couple of days ago, the name server for my site suddenly changed to something else. On my domain provider it is showing as the right one. For example this is what my domain registrar is showing

example.com ns7.abc.com <---------- this is the correct value

However, when I use nslookup, I am seeing something else altogether:

example.com dns1.xyz.com

My whois entry is indicating the incorrect value. The whois record continues to show the right owner of the domain though.

Has my domain been hijacked? How can I fix this?