Looking on the internet deeply has found these results:

i should not have said that is the most popular phrase on the web.

i should not had said that 11,160,000 results on the web	i should not have said that 11,250,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
You had said that you were not well... I thought you had said that he has a cocaine problem. His dad had said that it was unmakeable with you attached. Walternate had said that it was a very powerful piece of ancient tech. You had said that before, and then you changed your mind. Mother... you had said that you'll convince him. He also agreed with those MEPs that had said that the NPT had to revised. Not even Hitler had said that.	I should not have said that. Once, you would not have said that. You should not have said "Earth jokes." Maybe I should not have said that to homeless. I am afraid that the minister should not have said this in his intervention, because, on the contrary, we shall not achieve integration with less money, especially less necessary money. Now that you should not have said. He might not have said that thing about the kid right then. She should not have said that about your mother.

i should not had said that

11,160,000 results on the web

i should not have said that

11,250,000 results on the web

More popular!

I should not have said that.
Once, you would not have said that.
You should not have said "Earth jokes."
Maybe I should not have said that to homeless.
I am afraid that the minister should not have said this in his intervention, because, on the contrary, we shall not achieve integration with less money, especially less necessary money.
Now that you should not have said.
He might not have said that thing about the kid right then.
She should not have said that about your mother.