The purpose of prayer is to communicate with God. God hears every prayer, and he answers every prayer. If we fail to discern his answer, it is simply our lacking.
I have a good friend who suffered a heart attack over the weekend, and appears to be severely brain damaged. My prayer is that he will be fully healed and restored. God might do that, it is apparent that He is able to do that. But God might have a reason to leave my friend in a vegetative state, possibly for years. I don't understand why He would do that, but it has happened to others, and my lack of ability to understand why God would do something that my mind and heart do not understand doesn't mean God's reasoning isn't valid.
Isn't faith to a large degree simply putting our trust in God? I trust that if he takes my friend, that He had a purpose. If He heals my friend, that will be in line with His purpose, and if He allows my friend to linger, that will be in His purpose.
Whether I feel like he has answered my prayer, or if I understand why He is doing whatever He will do, He remains my Father. And I trust Father.
If God answers your prayer in the affirmative after all these years, there is purpose in it. If he continues to answer it by withholding what you might desire, there is purpose in it.
Trust the Lord with all your heart, even when understanding isn't evident. Peace to all