Hi,
That's just one of many reasons the Enterprise version is worth every penny. :-)
You could clean your database running a sql query in phpmyadmin if you are familiar with it.
Or maybe..... if you're very friendly and ask it very nicely you could try to ask support for help on a feature you're not paying for.... https://www.acymailing.com/support/. (I can't guarantee anything)
I don't work at Acyba, but from my point of view it would be fair if you upgrade to the Enterprise version. The pricing difference between Essential and Enterprise is only € 5 per month.