Have you had an MRI to try to determine the root cause of your plantar fasciitis? I was having trouble with severe symptoms back in 2009-10 and saw a specialist. The MRI revealed that two of the three ligaments on the outside of my left ankle anterior (talofibular ligament and posterior talofibular ligament) were completely torn. Reflecting back, I could recall two separate injuries that occurred in my recent past, either one of which could have been the root cause. Over time, my improper healing of THOSE injuries led to my plantar fasciitis. The doctor (Dr. Robert Lim) constructed two synthetic ligaments out of nylon and anchored them with titanium screws.
The point here isn't that I think you have missing or ruptured ligaments in YOUR ankle. Rather, I'm suggesting that the root cause of your plantar fasciitis pain may be from a related defect, potentially an undiagnosed ankle injury. It's worth looking into.
BTW: I was back playing softball in under 6 weeks. Rehab on conventional ankle reconstruction (even partial) used to be 6 MONTHS. This procedure was invented by the doctor that performed it, and I haven't had a single flair-up of plantar fasciitis pain since.