God is more than willing to heal the sick. It is not His will for anyone to be sick and neither is it His way of teaching us a lesson.
The fact that you have been disappointed is not enough for you to change your convictions. Stand like the woman with the issue of blood who waited 12 years to be healed and like Abraham who waited over 2 decades to see God’s promise fulfilled in His life. Don’t give up, God’s word is always true; the contradictions in your life notwithstanding.
Stop allowing the things that happened in your past to affect the miraculous in your now and future.