"What I did is" is correct. It does not matter that the doing occurred in the past: it is still what I did, and will always be what I did. The answer below represents a very popular misuse of tenses.
You are talking about something you did in the past, because you are using "did", therefore the correct statement is, "What I did was..." If you were to use the verb "is" or "to be" then that means you are speaking about the present, so the correct statement using this verb is "What I am doing is..."
"Not like that" can be grammatically correct, depending on the context.
The phrase "Is you don't miss me do you" is not grammatically correct. It should be rephrased to something like "Don't you miss me?" to be correct.
Yes! That is grammatically correct!
Yes, 'for free', is grammatically correct.
The phrase "You are not knowing" is not grammatically correct. Instead, you can use "You do not know" or "You are not aware."
Yes, Almighty God is grammatically correct.
"That was wrong" is a grammatically correct sentence.
Yes, it is grammatically correct.
The sentence "Rhoda's Crazy" is not grammatically correct. It is missing a verb to make a complete sentence.
'What a drunkard you are' is a grammatically correct English sentence.
"For free' is grammatically correct. It is an idiom of the English language.
The sentence is grammatically correct.