You must contact registrar and tell them to completely flush your DNS records on your account.
Set your nameservers to default, then visit DNS records advanced and DELETE ALL RECORDS, A RECORDS, EVERY RECORD DELETE IT.
Set your domain to ns1.hosting24.com and ns2.hosting24.com wait a little bit of time, go have some tea and a biscuit.
Now return and revert to registrar again, and now back to ns01.000webhost.com and ns02.000webhost.com
Using Google DNS, flush your DNS and then if needed wait up to 24 hours.
With some registrars I've had to call before and get them to manually erase hidden DNS records, it is up to them to fix issues on their end.