I'm from the Netherlands, so I'm not quite sure at what time the support is opening, so I thought I'll try it here.
Currently I'm trying to login with the data I got, but sometimes I just can't get in. And when I do get in the ftp account, then uploading takes ALONG time, because it constantly stops... and then it goes again.
Sounds like you may be getting temporary blocks placed on your IP address by the server firewall. Please try to limit the concurrent connections used by your FTP client. We've also doubled the concurrent connection limit on your server, so that should help as well.