How can I open the trunk with a broken latch?

You may be able to get to the back of the latch by crawling through the rear seat. You'll need to unhook one side of the lower cushion at a time. Push rearward on the bottom of the seat frame, then lift it up to unhook it. Once that is done on both sides, the cushion can be pulled forward. Remove it from the car.

Now you should see a pair of bolts holding the backrest to the body. Remove those bolts, then lift that cushion up off its hooks. Pull the top forward, then that section can be removed from the car.

There is likely to be a silencer pad still hanging there. Remove that to gain access to the trunk. Take a flashlight and a pair of pliers with you. There is usually what looks like the end of a flat-blade screwdriver attached to the lock cylinder. You can see that sticking through the latch assembly. Use the pliers to turn that piece to pop the latch. There may also be an emergency cable to pull once you're in there.

Please let us know if that works.