Generic supply line from the wall shutoff to the inlet of the fill valve come in different lengths. The standard braided supplys for toilets come in 9", 12" and 16".
For the ADA version toilets, most of the time a 12" will do and sometimes a 16".
For standard height, I use 12".
I would remove the supply from the toilet and see if the water is flowing from the supply line. First things first. Where is the last place where water was found.