Calendar widget uses old calendar

Thanks for reporting, and JD's comment shows it is still happening in August, so this one is very much alive. The same symptom is collected in the largest thread we have on it: calendar widget not refreshing upcoming events. Upvoting there is the best way to push it, since we go through requests roughly by upvotes, and it gathers the reports in one place.

There is a fix that works for most people, and it is not the calendar app's own data: Android keeps a shared calendar storage between apps, and it is usually the part holding on to the deleted event. The steps are under "I deleted an event, but it still shows on Niagara's agenda" here: Niagara's Calendar Widget.

Wah, you clearly went through that already, so please do not repeat it. Your report is a useful data point precisely because the usual fix did not stick. One test would tell us a lot: install any other calendar widget app, for example "Calendar Widget: Month/Agenda", and see whether the cancelled event shows up there too. If it does, Android's calendar storage is still serving it and the problem sits below Niagara. If only Niagara shows it, that points at us, and it would be very helpful to know.