From what you've said...
Just replacing a cable to permit 1 more phone (I assume from 2 pair to 3 or 4 pair cable) has absolutely nothing to do with the voicemail by itself.
However, if your father or whoever the "tech" was decided to play in the VM and try to make changes in the CCR tree, such as adding a separate branch for this new extension, then that would explain why it's messed up now. The tree needs to be "saved", but you can't do that until it IS complete.
From here, it's very difficult to see what he/she did to the tree to make it incomplete.
As stated before, get someone in there that knows what he's doing being you do something even worse.
You now have 3 options:
a) A few dollars now to set it up properly or
b) A few for aspirin for that acheing headache you're causing or
c) a lot more later after you mess it up far worse.
Your choice. There are times that even experienced techs have to admit that they are beyond their skill level. No offense, but you are at that point.
