Android Calendar app Problem: Shows DELETED calendars from Office 365 Exchange

Hello ladies and gentlemen,

I have quite a very disturbing issue: The stock calendar app from Android shows calendars that I have deleted previously.

Printscreen:
http://prntscr.com/82lwn3

dd, dd (2), CELCAT, CELCAT Timetable and Timetable should NOT appear, as they do not exist anymore!

I have made sure that my calendars are deleted from both the OWA website:
http://prntscr.com/82lxev
As you see, none of the calendars here anymore.

I also made sure they were deleted from the Outlook programme:
http://prntscr.com/82ly74
(I even cleared the Deleted Items folder). Do not mind the "Ημερολόγιο" & "Ημερολόγιο γενεθλίων", as they belong to another e-mail address.

So in my phone, I deleted the email address, cleared the cache and data from Outlook Storage, re-entered it and the calendars still appear. Office 365 Exchange will not assist with this matter, as it indicates that the calendars are deleted from their servers and that it is the app's/phone's issue.

A few information:

Phone: Elephone P7000 Pioneer
OS: Android 5.0 (Rooted & Modded)
App: Stock app for Calendar

Thanks very much!