Ah well!
I know. I get the same feeling.
Nevertheless
By definition a hard heart is an unbelieving heart; a heart that does not understand, a heart that will not listen. So Moses turned the waters of Egypt into blood, but that wasn't enough to make Pharaoh believe. Pharaoh didn't lay it to heart. So Moses sent another plague. Again Pharaoh would not listen to Moses and he would not acknowledge the LORD. Several plagues later Pharaoh acknowledges he was wrong and the LORD was right. But then he sins again. He doesn't let the people go.
Exodus 9:34
But when Pharaoh saw that the rain and the hail and the thunder had ceased, he
sinned yet
again, and hardened his heart, he and his servants.
Exodus 10:16
Then Pharaoh called Moses and Aaron in haste, and said, “I have
sinned
against the Lord your God, and
against you.
The point is Pharaoh's heart did not get harder each time Moses said 'Let my people go". The point is that even though the LORD showed him miracles and wonders, Pharaoh would not believe.
The interesting thing is Pharaoh agreed to let the people go several times, but the LORD would not let him believe. So after Moses lifted the plague Pharaoh hardened his heart.
By the way. I know you are not going to agree because the doctrine of freewill makes Pharaoh responsible for not believing Moses.