What must I do concerning my oath that I would not eat until I heard the voice of the person who accepted my apology, but he went to sleep?

You have broken your oath by eating before hearing the voice of the person mentioned, and thus an expiation for breaking an oath is incumbent upon you. The expiation for breaking an oath is mentioned in the words of Allah the Almighty: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever finds not [the means] - then a fast of three days. That is the expiation for oaths when you have sworn. And guard your oaths. Thus does Allah make clear to you His verses that you may be grateful." {Al-Ma'idah: 89}.