That's rather selective citation on your part. Let's look at the story of Pharaoh in its entirety:
| Exodus | Text | Agency | Source |
| 4:21 | And the LORD said to Moses, "When you go back to Egypt, see that you do before Pharaoh all the miracles which I have put in your power; but I will harden his heart, so that he will not let the people go. | God | J |
| 7:3 | But I will harden Pharaoh's heart, and though I multiply my signs and wonders in the land of Egypt, | God | P |
| 7:13 | Still Pharaoh's heart was hardened, and he would not listen to them; as the LORD had said. | Passive | P |
| 7:14 | Then the LORD said to Moses, "Pharaoh's heart is hardened, he refuses to let the people go. | Passive | J |
| 7:22 | But the magicians of Egypt did the same by their secret arts; so Pharaoh's heart remained hardened, and he would not listen to them; as the LORD had said. | Passive | P |
| 8:15 | But when Pharaoh saw that there was a respite, he hardened his heart, and would not listen to them; as the LORD had said. | Pharaoh | J |
| 8:19 | And the magicians said to Pharaoh, "This is the finger of God." But Pharaoh's heart was hardened, and he would not listen to them; as the LORD had said. | Passive | P |
| 8:32 | But Pharaoh hardened his heart this time also, and did not let the people go. | Pharaoh | J |
| 9:7 | And Pharaoh sent, and behold, not one of the cattle of the Israelites was dead. But the heart of Pharaoh was hardened, and he did not let the people go. | Passive | J |
| 9:12 | But the LORD hardened the heart of Pharaoh, and he did not listen to them; as the LORD had spoken to Moses. | God | P |
| 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. | Pharaoh | J |
| 9:35 | So the heart of Pharaoh was hardened, and he did not let the people of Israel go; as the LORD had spoken through Moses. | Passive | J |
| 10:1 | Then the LORD said to Moses, "Go in to Pharaoh; for I have hardened his heart and the heart of his servants, that I may show these signs of mine among them, | God | J |
| 10:20 | But the LORD hardened Pharaoh's heart, and he did not let the children of Israel go. | God | J |
| 10:27 | But the LORD hardened Pharaoh's heart, and he would not let them go. | God | J |
| 11:10 | Moses and Aaron did all these wonders before Pharaoh; and the LORD hardened Pharaoh's heart, and he did not let the people of Israel go out of his land. | God | P |
| 14:4 | And I will harden Pharaoh's heart, and he will pursue them and I will get glory over Pharaoh and all his host; and the Egyptians shall know that I am the LORD." And they did so. | God | P |
| 14:8 | And the LORD hardened the heart of Pharaoh king of Egypt and he pursued the people of Israel as they went forth defiantly. | God | P |
| 14:17 | And I will harden the hearts of the Egyptians so that they shall go in after them, and I will get glory over Pharaoh and all his host, his chariots, and his horsemen. | God | P |
Not only is it obviously God that as mentioned as the agent of hardening much more often than Pharaoh, but the first two mentions of Pharaoh's heart hardening are by God in which HE explicitly states His intent in doing so.
So was the last sin you committed something which God was helpless to prevent?