I had similar experience, it's just a lil tricky. I found it was easiest to boot phone completely, plug into computer, you hear the pc chime when phone is recognized, at that point hold the vol - and power until the pc chimes the disconnect, then immediately release the power button and tap the vol + repeatedly (usually 1-3 times) until the PC chimes connected, this all while still holding vol -. Practice how to hold the phone, release power and tap a few time and then it was easy.
Flashed back to stock. Flashed abl, xbl, xbl_config, laf and I had access to download mode. Back on stock. Thanks for your reply