it would appear that this is on some other hosting than the Piwik you mentioned as working, right? In such a case you need to contact admin supervising the server to provide Composer server-side.
@Michele_Marchi Composer shouldn’t be needed to run Piwik. Could it be that you downloaded Piwik from Github instead of the piwik.org download servers?
Then, what’s also possible is that the file upload to the server did not work correctly. (Because that message appears if the following file is missing: /vendor/autoload.php - either due to download from Github or due to an incorrect upload.)
I would suggest, to be sure, to repeat the entire procedure. I.e.:
Additional hint (not related to this issue, but to prevent files being shown as changed on Piwik installation check): Please always upload in “binary” mode, not the “text”/“ASCII” mode, if your FTP client allows for the latter.
Please be careful with that in future - please keep “/config/config.ini.php” in place when deleting all Piwik files. Deleting everything (including “config.ini.php”) has always (or at least for a very long time) worked, but won’t when updating to Piwik 2.16.0. You’d get https://github.com/piwik/piwik/issues/9666. The first response there provides a fix, if you run into it.