Jeebuz, it's 6 pages of advice and still no progress??
When I first received my ball python (about 75-100 grams), he wasn't eating either. He was housed in a 10 gallon tank. Maintaining humidity was difficult. I followed the sticky thread 101 hatchling advice and it worked! Boger provided that link to you somewhere at the start. Tubs also make maintaining humidity a breeze. Make sure to add air holes.
Imo, 20 gallon is way too big for a 200 or so grams ball python. Something about the size of a 6 or 12 quart tub should suffice, it's nice and snuggly for the snake. Anyways, listen to what Wilbanks said, it's probably similar to what was advised in the 101 hatchling thread.