This has happened due to a Junk / spam email that you have received,
it has annoyingly automatically set reminders within your calendar,
Please Note…
Before you take the next steps please ensure that you have all up and coming meetings and reminders saved aside from the calendar app in order not to loose them..
I found, the only way to get rid of this (without deleting the reminders individually) is to remove the email account from your calendar.
Settings> Calendar> Calendar Accounts> Tap the Account that the spam email was received from> Switch off the Calendar Tab..
The annoying reminders should all be cleared by doing this..
The only problem with doing this is that your calendar reminders will need to be entered / updated manually rather than relying on emails that automatically save the time and dates of business meetings on the calendar app.
I hope this helps guys!