Am I still irrevocably divorced from my husband, who divorced me on 23/4/1430 and had intercourse with me on 16/5/1430 during the 'iddah, even though he told me that I was irrevocably divorced by three pronouncements?

Divorce occurs the moment the husband utters it. So, if your husband divorced you with an explicit pronouncement, or with an implicit pronouncement accompanied by the intention of divorce, then it is an effective divorce. This divorce is revocable unless it was preceded by two divorces. Intercourse that occurs during the waiting period is considered a return (revocation of divorce) according to some scholars.

If you believe that he did not divorce you three times, and your husband did not divorce you three times, then you remain under his marital bond due to his return to you through intercourse. However, if he divorced you three times without any revocations in between, then the major irrevocable divorce (al-baynunah al-kubra) has occurred according to the majority of scholars, and you become unlawful for him until you marry another husband in a valid marriage and he consummates the marriage with you, and then divorces you. It is advisable to refer to a Sharia judge to resolve the dispute.