Same problem, but I managed to fix it :
First i disabled the plugin with SQL queries as described higher, here they are, but you need to change the prefix for the one used by your site :
UPDATE #_extensions SET enabled = '0' WHERE name = 'AcyMailing - Joomla integration';
Now the back office should be working again. So I went to install AcyMailing with the .tar.gz from https://www.acymailing.com/#download .
Then enable the plugin again and everything works !