Given how quickly it returned, I suspect it's not a case of some malicious hacker, but rather a bug in which the removal isn't actually "sticking". Is this you

Given how quickly it returned, I suspect it's not a case of some malicious hacker, but rather a bug in which the removal isn't actually "sticking". Is this your main/primary calendar, or a sub-calendar inside of your Google Calendar account? I ask because if it's shared perhaps it's a weird case where Google thinks there are two owners? If it's your main calendar (the ID is your gmail email address), then you should have full and absolute control over sharing for sure. Note: you can delete even your primary calendar (very bottom of the calendar settings), so before you stand up an entire new Google identity, you can also try that. Best of luck! (PS: I know stuff about GCal because I'm a cofounder of reclaim.ai)