My gentle way to get mine unstuck was to hook the tape with a dental pick and yank on it until it popped out. I think it's safe to say if there's a tape stuck in there now the mechanism is probably broken. Once you get the old one out I doubt you'll be listening to your old cassettes of the BeeGee's. Sorry.
Mine was stuck when I bought it last summer. I've transfered all my old tapes worth keeping on to CD's so really don't care especially with having a 6 CD changer in the trunk. So I just kind of ignore it.
I've had luck with a miniature flathead screwdriver, but not at the base where the pickup contact the tape. Rather along the side of the cassette, about where the gears/drivers are. It felt like I hit some sort of trigger and then the cassette popped right out.