I also had resistant hypertension, much as you describe, for many years. There are at least 3 relatively uncommon conditions that can cause this, that can be tested for: renovascular hypertension, hyperaldosteronism, and pheochromocytoma.
I was found to have renovascular hypertension. The solution was to put stents in my renal artery. I still have to take 4 BP meds but now I have normal BP. I am so glad I had this done.
Sleep apnea can also cause hypertension.