Does divorce take effect by swearing to it with the strong belief that the papers were not received, and then it turned out that their receipt was forgotten?

Since you swore, believing yourself to be truthful and not intending to lie, the preponderant opinion is that you have not broken your oath and no divorce has occurred. Divorce does not take place in this situation. This is the correct view among the sayings of the scholars, as it is in the category of a "null oath" (yamin laghw).