It's important to remember that DNS settings take TIME to propagate whenever you make a change. The changes you make are reflected at the Root Server level either once or twice daily (depending on the Registrar) and then they gradually "fan out" across the Internet (the process is automatic!).  This propagation delay is generally out of your Registrar's hands - it's essentially a function of the DNS system itself - so angry emails to tech support won't help. The only cure for DNS resolution problems once you've made a change (as long as you're sure your Registrar has recorded the change) is to wait until the change filters through to all corners of the Internet.