How do i delete and stop spam events appearing in calendar

I've recently been inundated with spam events adding themselves to my calendar from unknown senders, on both my iPad and iPhone

As advised in previous posts, I've tried to create a separate calendar to add these events into to then delete; however, when I click on the event and select to change the calendar nothing happens. The button animates as if it has clicked but does not open a selection to change calendar

I've also tried finding the events in Calendar through my iCloud in a browser from my MacBook; but cannot see these events in the iCloud calendar

Any ideas on how to remove them and stop them coming in would be really appreciated!

Thanks

M