Hi Wilson, can you write a sample sentence of how you used it? It might be more clear. Just looking at "i haven't it" by itself I think you are missing another verb. For ex. "I haven't seen it" or "I haven't heard it" in these examples "have" is part of the present perfect tense of the verb and needs another main verb to go with it. When we say "I do not have it" , have is the main verb and doesn't need another verb after it. It does need a noun after it. ex. "I have the book" "I do not have the keys."

I don't know the actual grammatical corrections, but I think I have not (haven't) is usually followed by a verb or action. I do not have is usually followed by a noun or thing. example. I have not said it, I have not done it, I have not written that I do not have this, I do not have chocolate, I do not have shoes

Thank you for your answers. The both was very good for me. I helped me a lot.