It doesn't sound like the issues you're having are caused by the software, but if you think it's corrupted, you can download a fresh copy from Machsupport.. You can also buy a valid license directly from them. Mach3 will work in demo mode for 500 lines of code, without a license being necessary. Then it will quit.
Who built this machine for you? Sometimes a little "naming and shaming" will cause companies to rethink their actions. Was this company in the same country as you, or is it overseas? In the former case you might have some recourse; in the latter, not so much.