have you solved your problem? I am faced with exactly the same issue.
When deactivating Piwik’s Provider plugin as recommended in FAQ No. 180 all provider information is lost.
When re-activating the Provider plugin I can retrieve the ISP information (which is sometimes replaced by the organization name) but there seems to be no difference to the situation before integrating the MaxMind databases. As suggested in FAQ No. 180 Piwik’s Provider plugin overrides the information provided by the MaxMind databases.
It is possible that this feature has regressed and not work as well as it used to. Could you please create abug report with your information on our issue tracker? Issues · matomo-org/piwik · GitHub
With an issue in our tracker, we will investigate in the coming weeks, thanks