Wrong PHP version after upgrade

Someone upgraded our WordPress to current version. Afterward, all web pages including wp-admin started displaying Your server’s PHP version (5.5.9-1ubuntu4.25) is not supported.

I thought this would be an easy fix – I installed PHP7.0 and restarted, but the pages are still displaying the same message.

php -ver reports PHP 7.0.31, but WordPress doesn’t seem to “know” that there is a new PHP installed. Where can I look for to correct this? Keeping in mind that the admin panel doesn’t run any longer.