I see what you are saying, I too struggled with that, but if you look close at those verses you posted it says "for God is able to graft them in again". And right now the Jewish nation as a whole is still in that unbelief against the Christ, but if you look at those prophecies they were no longer unbelievers when that point of repentance comes. And I believe that is how He grafts them back in again.
"And I will pour on the house of David and on the inhabitants of Jerusalem the Spirit of grace and supplication; then they will look on Me whom they pierced. Yes, they will mourn for Him as one mourns for his only son, and grieve for Him as one grieves for a firstborn."
"For I tell you, you will not see me again until you say, 'Blessed is he who comes in the name of the Lord.'"
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