You have to make sure you actually run a nameserver on your VPS, and that your zone is added.
You also need to register your nameservers with the registry (your registrar)
If you don't run your own nameserver, then you can use www.afraid.org
for free DNS, and you would add the domain and put ns1.afraid.org and ns2.afraid.org into the registrar.
Lastly if this betterhost.ca is hosting your DNS the best course of action is to ask them what their nameservers are.
Reason I'm making this a tad complicated is because at least I feel you didn't post enough information about your exact setup.