FTP - cannot connect to plushost server

[#1]

This is very frustrating - I cannot connect to my PAYH web server. I'm using a Mac and FTP client Transmit. To check it wasn't Transmit at fault I also tried connecting with Cyberduck. No luck there either. I'm using the server address given to me at signup of: ftp.username.plushost.co.uk and this appears to be right. I can see all the web files in the Plesk control panel in the directory of httpdocs - which is where I put them in December. PlusNet haven't been too helpful so far (a) directed me to the help page 'how to ftp' (no comment) and (b) referring me to the appropriate team - which I take to mean Kevin Mawson, who seems to be running this show. Anyway, can anyone perhaps let me know what I'm doing wrong - or say whether there is a glitch at the PlusNet end? Thanks.
PS. The message I'm getting is: Could not connect to server "ftp.oldgustav.plushost.co.uk" - server not found.

[#2]

Hi
What happens when you attempt to FTP in to the space?
Please note your FTP username will be different to the main user name. To find this out, log in to the Plesk control panel, click home, then on to the domain and then on to Setup (under hosting). From here you will be able to see your FTP login and you will be able to set the password to use.
Let me know if that helps.

[#3]

Hi Kevin, Thanks for the reply. When I enter 'ftp.oldgustav.plushost.co.uk' into I get the little yellow warning triangle indicating that something is not right (see attached).
I know about the the variations on the user names for each domain - but I'm not getting as far as that.

[#4]

Hi
I can see that you have turned that domain off in your control panel, you should be able to use ftp.your domain name
As the plushost domain has been switched off it doesn't write the dns for that domain.
That should hopefully work

[#5]

Thank you very much Kevin. That work perfectly. Sorry to trouble you and for being an amateur IT twat.