i do not recall which fuse powers the relay with the bell (dinger).
you likely have a short somewhere on a system using that fuse. either someone else will tell you which fuse that is or you can get it to ding then pull one fuse at a time until it stops dinging to locate the circuit. then test each system on that fuse for the short.

the rear hatch lock will need to be completely removed, cleaned for rust and corrosion then greased and re installed. but then you already suspected that by thinking force could supplant judgement. now you have to fix it. try opening it from the inside. if it won't you'll need to remove the fabric panel on the inner tailgate and work from there to get it open. how to fix the tailgate locking latch will be self evident once the gate is open.

it is unlikely the key cylinder on the tailgate needs work so leave that part alone.