Which one is correct?
I've come to see you and now you have to listen to me.
I came to see you and now you have to listen to me.

Question

Which one is correct?
I've come to see you and now you have to listen to me.
I  came to see you and now you have to listen to me.

Answer

Both are grammatically correct.

Depending on the context, either of these form is appropriate.

Answer

Both are correct, although they have slightly different intonations.