Lifelong disease with approved intermittent FMLA being denied 12 weeks

Over two years ago I was diagnosed with a lifelong disease completed paperwork and was approved intermittent FMLA. Close to my one year anniversary was told we work on a rolling basis and my days would replenish as I hit the anniversary of that day. Later HR came back and said my days would only replenish if I had a release. I have a chronic lifelong illnes and will never have a release. It has been a year and a half since I returned certification (which HR says is still valid)and over two years later am still being deducted from the original 12 weeks granted over two years ago. We get full pay during our 12 weeks but have been told I only have a few days left and will not get full pay. Is this a violation? How can I be using the same 12 weeks from two years ago? How can I return a release? I will have this disease the rest of my life?