Hi,
I don't know why the download doesn't work for you, it works perfectly on my end.
Please copy your license key. In Acymailing->Configuration->License unlink your license key and save your configuration. After that add the license key, link your license and save your configuration again. Finally activate your cron and save your configuration again.
If this does not resolve your issue, please raise a support ticket https://www.acymailing.com/support/