Hello Andy,
Can you please include a snapshot of "Manage DNS" section and "Nameservers" section of your 123-reg control panel ?
We are here to help you and there's no need to feel bad for contacting our support team. We want your
website hostings to work smoothly as you are our customer and if it takes solving 123-reg problems then we have no issues in doing so
DNS changes take few hours so if you check nameserver status immediately then you won't get any results. Make sure you add A records for respective nameservers on your
VPS Hosting as well as the nameservers won't work if they don't have A records on your
VPS Hosting.