iCalendar Spam on iPhone

My calendar has recently been filling up with spam notifications. There is no option to delete them and these calendar events don’t show up on my iCloud calendar so I can’t delete them on my computer/the iCloud website. They disappear once the event finishes, however reminders show up twice before the event begins even if I delete the reminders, and everyday more than 5 new events show up again. Please help? How can I stop this ??