Forced reminders

The extra reminders that you are getting could be initiated by other calendar apps or from Google Calendar. Make sure you have disabled all the notifications in the settings menu in other calendar apps.  Also check if you have removed the event reminders in the web interface of Google Calendar.

Go to www.google.com/calendar

 Disable notifications for all events on a calendar

If you wish to disable all of the event notifications for a specific calendar, please follow these instructions:

In the calendar list on the left side of the page, click the down-arrow next to the appropriate calendar. 



Select Reminders and notifications



Click the remove link next to each reminder set in the Event reminder section.



Then, deselect any selected boxes in the Choose how you would like to be notified section.

Click Save.



Note that default notifications are set per calendar, please make sure you have disabled them on all your calendars.

Please note that when you make changes to the reminder settings for events on your calendar, the changes will only apply to you. Invited guests or those who have access to the events will receive reminders according to their own Google Calendar reminder settings.

Source: https://support.google.com/calendar/answer/37170?hl=en&ref_topic=1672527