Thank you for the answers. The problem is, we cannot create a folder nor upload a file using FTP, knowing that we have successfully logged on. It was working pretty normal until thing suddenly stopped functioning correctly and we get FTP errors saying that we're over quota (which we're not) ! here are some screenshots from WordPress, FileZilla and 000webhost file manager.
Upload from wordpress : (http://acemadvault.000webhostapp.com/)
Upload from filezilla (directory creation) (as you can see 8% inode usage and 2% disk space usage, and still saying over quota ??)
Uploading using 000webhost file manager; same error disk quota exceeded while uploading a simple image.
I believe it's an FTP problem and not a wordpress issue, please help us with this.