Almost anyone who has ever had a tape player in their car
has had this problem at least once.
There are at least two main causes for it:
1. A "dirty" capstan can wind tape around itself until it jams against the
cassette housing and/or it pushes the pinch roller as far away as it will go.
Either way, the tightly-wrapped tape prevents the
cassette from being disengaged from the machine.
2. The mechanism involved with the "cage" that holds the cassette
while it is in the player can get stuck and prevent tape removal.
There are some other, less-likely possibilities.
The unit should be removed from the vehicle, and after the
tape has been removed, any other needed service/repair
should be done. The final step is to clean and demagnetize
all the parts of the machine that the tape touches.
I recommend having this done by a good repair shop.