OK so Pharaoh knew the history of Joseph and his family. He well knew about the 14 year prophecy that saw 7 years of massive crops followed by 7 years of famine that devastated the economy and saw the government buy all the land etc... from their citizens.
When he stated he did not know the Lord it was a statement of defiance, not one of truth. Moses was also well known to him as Moses was raised in Pharaoh's palace until the age of 40 although it would have bee...n a previous pharaoh. Since being pharaoh was an inherited position you can be sure they knew each other well.
Now there were 10 plagues. 10 times Moses asked for the Israelites to be released. 10 times pharaoh refused. After each plague pharaoh always promised he would release them when the plague was lifted. Each time he went back on his word. The economic pressures were too great. The impact it would have on his rule and the nation was one he couldn't imagine recovering from.
What we must remember is that Pharaoh like every other human being had choices. He was not a puppet.
Of the 10 plagues you will note that 5 times the Bible says God hardened pharaohs heart and 5 times it says pharaoh hardened his own heart. You can't harden your heart unless you are a free moral agent.
The question is what does it mean when the Bible says God hardened his heart? It means God needed pharaoh to allow the people to go and since he was determined to keep them as slaves he had to be pushed. Being pushed to make a choice is not being controlled. Being controlled means you have no choices.
Esau had choices, Pharaoh had choices, the priests and scribes had choices when they met Jesus. We all have choices. God knowing our hearts will use our choices, good or evil, for His ultimate purpose of saving as many of us as possible but He never will make our choices for us. The cross is proof of that. Jesus had to choose to die and that choice was to free us to even have options. We were destined for death with no options. Jesus bought back our freedom. He chose love for us over self preservation. Pharaoh chose self preservation. Ironically self preservation leads to death while dying for others leads to life all the way around.
Paul is devastated in chapter 9 because he can see his nation making the same choice pharaoh made...
Remember what Joshua told the nation just before his death? "Choose you this day whom you will serve... As for me and my house we will serve the Lord!"