The Navigation/DVD slot will only accept one disc. Once there is one in there; whether it's a CD or DVD; it will not accept another one. Perhaps you are talking about the CD player, which will accept 6. There is an eject button to get them out. There are some who have had problems getting discs out. Do a search on here to find the thread(s) dealing with this subject.
The DVD slot is behind the display.
The CD slot is the one in the center console below the stereo.
Regardless, if "eject" isn't working, find the 2 fuses for the stereo and remove them both for 10 minutes, then put them back in and see if that helps.
My four disc set of The Police complete collection is safely locked away in my in-dash six, maybe never to be played or to see the light of day again. At least I don't have four CDs stacked one on top of the other in the DVD tray...