Pull the inside hatch panel. The lock mechanism is located over the sill in the hatch. Prying on the fiberglass hatch is probably a great way to replace the whole thing.
Once the panel is off, you can see the mechanism that holds the latch lock closed and pop it open to release it from the striker bolt. You'll also see what's going on why it won't operate - cylinder frozen, broken tabs, missing parts, debris jammed in the striker, etc.
There's also the chance the hatch is dropped and jammed in place. Pushing it open with your feet will be easier inside that tugging on a small finger pull.