We use "so much so that" with the meaning "to such an extent". We use it after a statement to reinforce it using an example showing how much this statement is true.
We use "so much for" to express disappointment at the fact that we won't be able to do what we wanted to do, or that something is not as we thought it was.
In the pictures below, you will find some examples that will help you understand how to use these two expressions.

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