Question: Has the web site moved servers/ISP's ?

If so, you need to make sure that the old host/ISP has removed the DNS records & Website from there servers!!

Otherwise, you could be in a situation where once of our clients was. 3 months after there "new" site went live, people on iiNet were still seeing their OLD website. Anyone else with any other ISP saw their new site. The client had not advised iiNet (and we legally cannot action this on their behalf) yet of course the clients first course of action was to blame us....

ipconfig /dnsflush only flushes the DNS cache on the PC you type it. And all that essentially does, it remove any cached entries of names-to-ip resolutions (e.g. google.com = 66.102.11.104). If the site has simply been overwritten by a newer version, the effect should be instantaneous unless it is being cached by your ISP. This should sort itself within 12-48 hours max.

Try using an online web proxy to see what version of the website it sees.

Server teams are generally nightmare to deal with, unless you speak geek - Even then, sometimes you have to deal with the helpdesk monkeys who dont know their ass from their elbow.....