If you are currently unable to hear them then do not worry they will teach you through omens and intuition. When you evoke Belial for learning from him do not expect a physical manifestation Because that does take years of practice and effort. But This will be more of a connective evocation where you will recieve your teachings through omens, intuition, you may get a sense of understanding, you may only feel a vague hint of your answer, and all of this is dependent on your natural ability and the efforts you put into practicing evocation. Your results will become more noticeable as you progress with each evocation. It is better to have a strong connection with a particular demon if you are planning to evoke him by learning about him, creating a substantial contact. The more advanced your connection to the demon is, the more it knows and and senses you and the results will be more profound.
For when you evoke Belial pay attention to your intuition because it will be coming directly from the demon. Don’t worry if you can’t hear or see them yet your evocation will still be successful and you will form a direct communication with the demon, emotionally and mentally. You may hear The demon speaking through your mind, so pay attention to everything. Even if nothing of this happens he will surely will teach you through omens and intuition and as you practice evocation more and more so your ability to communicate will improve.
I will also advice you to practice getting into trance that way it is more easier to communicate with them.