Audio not loading (.mkv)

A customer sent me a .mkv file, and it told me that the audio should be separated when importing the file (Having voice and music separated). My computer even managed to load a 5 hour 4k High Resolution video with no problem and import it and export it with no sweat. And I already worked with a 4k video importing it directly to Premiere and it did imported the video and all the audio in different tracks (and this one was a 5 hour video).

I'm facing 3 problems with this file:

1) Premiere can't load the audio, I left it open throughout  the day with no other program running in the background to see if it's capable of loading and it just gets stuck on the same part (Preparing audio 50%) so I'm uncapable on listening the video.

2) When I import the file, this one should have all the audio tracks separately. Yet, it's importing all in one line.

3) I tried to delete the video from the project (to see if trying again would work) but when I do, Premiere stops working and it crashes. So if I want to remove it I need to create a new .prproj without the file (Start all over again, yet the problem still persist).

How can I fix this?