Is it correct to say this sentence?
I would have had written to you had you given me your address.
When do you use “have had”?
It is never correct. This is another mistake in which the helping verb “have” has been repeated.
We use “have had” where “have” is the helping verb, and “had” is the main verb. I can’t think of any situation in which we’d use “have” as a helping verb twice for the same main verb.
Thank you very much for explaining it to me. I guess I have been using the phrase because it sounded good to me. I will refrain from using it from now on.