At times, you may get issues like, the cpanel login details may be working, but the same won’t work for FTP. As you are aware, cpanel and main FTP login details are always same. Resetting the password may not help in this case. Then check if a file named /etc/ftpusers is present in the server and if your username is included there. This files blocks FTP access for the users listed in it. Remove your user from there, if present and you can regain FTP access