My calendar

Your calendar is lying to you.

If running iOS 13 or earlier versions, check: Settings - Passwords & Accounts - Accounts - Any rogue entries here? If so, delete the rogue account. 

If running iOS 14, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

using iOS 14?

go to Settings > Calendar > Accounts, find the spam calendar and delete it

If using iOS 13, I believe it's in Settings > Passwords & Accounts