Okay, crazy suggestion:
Can we assume that, at this point, you've racked the slide several times and that the magazine is empty? Is it possible to remove the mag follower and spring while the magazine is in the pistol? If you can manage to get the follower and spring out of the mag tube, you might be able to reach down into the tube and push on the mag catch where it engages the mag tube.
In fact, you might be able to just depress the follower far enough to at least see what's going on inside there.
The Government 380 has a tiny rotating toggle that retains the mag catch in the frame, just like the 1911, doesn't it? Have you tried rotating that little catch lock (looks like a slotted screw head in the right side of the magazine catch, but it's not a screw) while manipulating the catch to see if the catch lock perhaps got rotated just a bit and is blocking up the operation of the mag catch?