If God exists then why have I never seen him or heard him?
From your question, it appears that your concept of God is not the same as the biblical description of God. In Hebrews 11:3, after the writer tells us that faith involves things which cannot be seen, he then tells us that, “By faith we understand that the universe was formed at God’s command, so that what is seen was not made out of what was visible.” In other words, the God of the Bible is not a visible God. He is not made up of physical stuff. In fact, God made all of the physical stuff of the universe, but he is not physical and he is not created.
This is why you cannot see God. He is not like some sort of old man with a beard in the sky. This is not the biblical God. He is spirit. Like Jesus said to the Samaritan woman at the well in John 4:24, “God is spirit and his worshipers must worship in the Spirit and in truth. God does not have literal hands or a face. He cannot be seen, although he has on occasion created a sort of “appearance” for example to Moses in Exodus chapter 3. God can create a visible manifestation if he so chooses, but this is not what he normally does.
Also, unlike in Exodus 3, when God spoke directly to Moses, God does not normally speak directly to us. You will not be hearing God speaking to you in audible sound. On rare occasions in the Bible God does create actual audible sound, for example on the Mountain of Transfiguration in Matthew 17:5. Again, this is the exception, not the rule.
If you want to see God, then you should look at Jesus in the gospels. John 1:18. “No one has seen God, but the one and only Son [Jesus] who is himself God and is in closest relationship with the Father, has made him known.
If you want to hear from God, the best way to do that is to read the Bible. In the Bible, God speaks to us in inspired words. “All Scripture is inspired by God.” (2 Timothy 3:16).
So, if you want to “see” God or to “hear” him, you can do this by reading the four gospels and by reading the Bible in general.