Geek-9pm might be right about a need to complain, but it would be best to be sure what exactly your complaint is going to be.
From what you wrote about something your uncle did there may be a problem with you right away calling the tech folks to look at things. They may make the claim that you tampered with something that shouldn't have been tampered with. They may not care about an excuse that you didn't do it — that your uncle did it. And that claim they make against you could allow them to add a lot more extra money to any bill they present you with.
Anyway, what's the rush? Just take this step-by-step and see where this goes.
And that's where I think we are right now — where does that line that comes out of the ground go? Directly through a wall into your house?
I know you wrote you've got one phone line that goes straight outside and goes into the ground, but let us confirm the situation coming from the other direction, please. The one line comes out of the ground and is eventually somehow fastened to a wall and crawls across the wall, so to speak, and at some point goes directly into that same wall and into your house? No images, please, as I get uncomfortable with folks posting images of their home on the Net, because it may not be so smart from a security point of view.
So maybe you could describe how that line/wire is fastened to your home after it exits the ground? How long is the line before it enters through some sort of hole into your house?
And the hole it goes through looks like what? Professional type of look to it? Has a kind of sheath protecting the line as it enters the house?
Then the next thing would be to explain what you see inside the house right at that spot where the line came in? Does it come out of the wall at the exact spot where it entered from the outside?
As to the last post Geek-9pm did about simply using the jack itself and not any of the actual wires, I agree. Should be no need to use the wires unwrapped from a wire bundle.
But I don't understand the need for a splitter for the line to the phone. I thought there was a plug/socket/whatever on the modem that went to the phone and another that goes to the computer. Only time I have used a splitter was when I have had more than one computer hooked to the modem. But things may be different in other countries.
So, yes, using the jack/plug/socket (whatever it's called) should be first choice over using wires unwound from a wire bundle.
BUT I think you are still going to have to figure out this businees of not being able to find the NID. That one may come back to bite you in the *censored* at a later date if you ignore it because you got better Net connection speeds. Something about that seems sort of weird. And if you go messing about with telephone company lines I think legal problems may pop up. But I am no Perry Mason and that idea may be way wrong.