I see it's a 1995 HR Navigator from looking at your profile. Since it is that old perhaps the seals are rusted to the flanges. That may mean you can release it by placing something flat into the seal area and slidding it around the perimeter to break the seal. This may mean the seals will break and be damaged. So as long as it opens you will then have to deal with replacing them. I would use a kitchen butter knife and with a sawing motion it should do the trick. Unless some other reason is causing it, as experienced by a HR owner on this sight, that's about all I can come up with for logic of the handles being opened and it still not releasing. Good luck.