DNS Help with Domain Mapping Plugin

Hi there,
Having a bit of a nightmare with domain mapping.

To fill you in, today I've started the move from shared hosting to a VPS. I'm new to owning a VPS, but, I've followed tutorials thoroughly. Here's briefly what i've done:
- On my VPS, I've set up my own nameservers - let's call them ns1.nameserver.com and ns2.nameserver.com.
- With my domain name i've changed the nameservers to the above.

My domain now works, and doing a DNS check shows my VPS IP address attached to the domain. However, in domain mapping, the plugin is picking up my old IP address and thus none of my sites that are mapped are working.

Any chance you can help me figure out this issue?