I ma having a problem with this too. I cannot believe that after all these year Samsung just hasn't gotten around to "fixing" this. It is clearly designed to be a pain in the ***.
When I go into Application Manager, the option to disable Calendar is disabled. I can clear the data and the cache and force stop, but I cannot disable.
When I go into account sync, "Calendar" is not there. It doesn't show up at all. I do see all of the other expected sync options, just not Calendar.
I have installed Google Calendar but it will not connect to my accounts, Samsung has broken this with their PoS calendar app. I just want it to so away.
Is there some way to delete this app? Or do I just need to take this phone back and get a refund then buy a real working Android phone from Google?