Soln: To prevent users from using the old url, we had to do a redirect like so on the same default.aspx page:
<asp:Content ContentPlaceHolderId="PlaceHolderAdditionalPageHead" runat="server">
<META Name="CollaborationServer" Content="SharePoint Team Web Site">
<script type="text/javascript">
//add here:
var url = window.location.href;
if(url.search(/servername:1234/i) != -1){
window.location="http://servername.co.com:1234/default.aspx";
}
//
var navBarHelpOverrideKey = "wssmain";
</script>
</asp:Content>