The "Finding Control Channel" isn't just a digital thing - it's also something you'd see with analog trunked systems.
If you have tried just about everything, I suggest you create a search where your scanning is searching the frequency range where the control channel frequency should be. You are wanting to hear something like a "machine gun" or "motor boat" sound. When you hear this, and you may hear several frequencies with that sound, write the frequencies down. Then program each one in your scanner and see if that is the correct control channel frequency.
Also, hopefully, while you are doing your search, you may hear voice traffic for your system. That will confirm you are in range of your system and probably are not being affected by interference.
Yet another option is if you can get mobile with your scanner. Go to within 1/4 mile of the transmitter site and see if the "Finding Control Channel" goes away. If it does, that means something around your home is keeping you from properly receiving the control channel.