Nameservers not updating

Hi there, I tried to reset my nameservers back to default last Friday (3 days ago). I have set them back to the default ones (ns1.mdnsservice.com, ns2 and ns3). This does now allow me to change the DNS settings, but, looking at the who.is records, the nameservers are still dns31.cloudns.net, dns32, 33 and 34 and haven't been updated?

Can you help please as we are trying to point to a new website and this is being held up by the nameservers not updating.

Thanks very much.