aCalendar does never add spam to your calendar!
If you receive SPAM notifications or you see SPAM events in your calendar, these are most likely added automatically by Google Calendar from incoming Gmail spam.
For more details about this, please see one of these links:
Starting with version 2.2.4, aCalendar has its own spam filter (as Google has not fixed this issue, though it is known since at least 2016).
If you still see spam with this version please send us details/screenshots, so we can improve our spam filter.