Sounds like you have already done a good diagnostic so if you can't fix the cable, no one here can either.
If there a way to get a new cable to where the receiver is located? It does not need to come from the same location. Depending upon where the receiver is located you could run it from a storage bay or the firewall or even feed it through a slide rubber gasket when you are parked. Since the original cable never worked properly I would at least just look at each end of the cable connection to see if it's loose or crushed. You can't make it any worse than not working and you might find a bad connection. You might also want to test to make sure it's wired right and that the satellite coax and Cable coax were not reversed.