This sounds like a propagation issue...seems like I ran into this a while back when my host had to change some of my ips.
I've been in a bit of hosting hell today myself...so I feel your pain. But, if I recall correctly...there's not a lot your host can do about an ip taking time to propagate.
Frustrating as hell for sure though
That said, Chop is right on the mark! Having a really good working relationship with your host is critical in this business. That box is what pays the bills after all.