Update All Rates not working

I recently installed the paid version of your plugin. The rates are not updating when I click ‘Update All Rates’. I had the WP Super Cache plugin activated and to make it compatible, I followed your instructions and installed Country Caching For WP Super Cache. But that plugin didn’t work properly (it couldn’t find the Maxmind file; that plugin was last updated two years ago from the plugin authors). So I uninstalled and removed WP Super Cache plugin entirely. However, I still can’t update the rates. I also have deactivated my Autoptmize plugin, but the rates still don’t update. I’ve tried everything but the rates do not update. Can you help?