Check you are connecting to the right IP address
BT Internet and Plusnet in the United Kingdom (but other providers in other countries may have similar restrictions) have a Parental Control feature which is known to interfere with the connection to our FTP servers. Specifically, they block DNS queries to the FTP server name ftpupload.net.
You can check whether this is the case by checking the logs of your FTP client. If you are using FileZilla, and everything is working as it should, you should see a line like this in the logs.
Connecting to 185.27.134.11:21...
If the line shows a different IP address, it means that DNS lookups to the ftpupload.net hostname are being intercepted on your network and blocking you from accessing the FTP server.
You can work around this by using the FTP hostname ftp.epizy.com or using the IP address 185.27.134.11.
Disabling the Parental Controls on the connection should also allow you to connect to the FTP server without issues.