After upgrading to 3.0.3 I got the message that my provider is running php 4
The requirement for PHP version 5.5.9 started with 3.0.0. Only Piwik 2.x is compatible with older Piwik versions. Unfortunately there is no way to downgrade a major release so you’ll need to restore a backup.
But there is still a problem left: PHP 4 is horribly outdated. The development stopped in 2008 (9 years ago). Even 5.5.9 is quite old (released in 2014). Please look for another provider who is using a php version that is still supported: PHP: Supported Versions