Answers
Why has God not answered my prayer?
Scripture gives several honest reasons and does not pretend there is only one. Sometimes the answer is no because the thing asked for would harm. Sometimes it is not yet, and the waiting is doing work the gift could not do. Sometimes there is a known sin or an unresolved quarrel in the way, and Scripture says so plainly. And sometimes, as with Paul's thorn, the answer is grace instead of removal, and that stays the answer. What is never true is that God did not hear.
Go and see for yourself
And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me.
2 Corinthians 12:9
Ye ask, and receive not, because ye ask amiss, that ye may consume it upon your lusts.
James 4:3
If I regard iniquity in my heart, the Lord will not hear me:
Psalm 66:18
And he spake a parable unto them to this end, that men ought always to pray, and not to faint;
Luke 18:1