In some cases, the server will not allow FTP over the server, the issue might be due to the enforcement set in the server.
Login to the server as root, for this you may need the SSH access to the server.
Run the command getenforce in shell.
If the output is enforcing,we may need to change to permissive as server allow FTP if it is set to permissive.
[root@server public_html]# getenforce
[root@server ]# setenforce –help
usage: setenforce [ Enforcing | Permissive | 1 | 0 ]
[root@server ]# setenforce 0
[root@server ]# getenforce