CANNOT LOGIN because of DEFENDER

For some reason this morning I get the following error :
Fatal error: Call to undefined method DateTime::diff() in /homepages/20/d414499459/htdocs/catalogue/wp-content/plugins/wp-defender/app/module/audit-log-module/component/class-wd-audit-api.php on line 54

I cannot even log in in order ti deactivate the Defender plugin .... What can I do ? I