you've got yourself in a pretty shitty situation if you managed to softlock it and saved in that state... you can try any one of these
1: reset events and objects and wipe your map... not recommended but if you absolutely have to you can at least fill the mailbox with your essential items first so they carry over
2: get outside the fence and climb up to it with a hook (preferably a half hook) or
3: rig up an airship with something like a bench and balloons (hopefully you already have nails, a hammer/nailgun, and balloons if you want to try this route, otherwise you gotta get some on a different save and put them in the mailbox) and fly up to it
4: back up your save in appdata>local>votv>saved>savegames, then change the prefix of the offending save to b_savenamehere if you've unlocked sandbox mode; if not, I don't think this will unlock it, and if you do have access it will remove a couple easter egg items from the map for some reason. Press V to fly and head over to it and free it, go back home, save, and revert the prefix of your save to s_savenamehere.
Viewing post in Voices of the Void 0.7 (Latest Release Build "0011") Bug Reports
damn if cheats aren't even working, you're gonna have to look up if anyone's figured out how to clip out of the invisible wall in this version yet, ways out get patched every update
if you've backed up your world you could try to use the delete command on the hook itself? (cheats in sandbox are accessed with 0 on the numpad), but beware you can delete literally anything and everything with it, including the map itself if your cursor is overlapped with the terrain at all