Some Mormons are visiting him and trying to make him doubt his religion
Question

                I am a muslim, but have the unfortunate blessing of living in the USA. I go to a school where my beliefs are daily insulted by the christians. Recently mormon (The Church of Jesus Christ of Latter Day Saints) missionaries have been repeatedly coming to my house and their evil children harrassing me at school. It doesn't matter if I say no, they believe they will be saving my soul. Are they even christians or some lower cult scum? They say if islam is so right to refute their own scripture, the book of mormon. How should I go about doing this or should I even at all? Thanks.
Praise be to Allah.My dear brother, you have 
          to know with absolute certainty that the religion of Islam is the true 
          religion which is pleasing to Allaah, and that Allaah will accept no 
          other religion from anybody apart from Islam. Islam is based on the 
          worship of Allaah Alone with no partner or associate, and on following 
          the Messenger Muhammad  (peace and 
          blessings of Allaah be upon him). This is the implication of bearing 
          witness that there is no god except Allaah and that Muhammad is the 
          Messenger of Allaah.  
If these beliefs are firmly entrenched in 
          the heart of the Muslim, he will not care about any opposition or mockery 
          on the part of others. Rather he will pray to Allaah and act in accordance 
          with the religion of Allaah, and he will say, “I am one of the  
          Muslims.” Allaah says (interpretation of the meanings): 
“And 
          who is better in speech than he who invites (men) to Allaah’s (Islamic 
          Monotheism), and does righteous deeds, and says: ‘I am one of the Muslims.’” 
          
[Fussilat 41:32] 
          
“Therefore proclaim 
          openly (Allaah’s Message   
          Islamic Monotheism) that which you are commanded, and turn away from 
          Al‑Mushrikeen (polytheists, idolaters, and disbelievers). 
Truly, We will suffice 
          you against the scoffers, 
Who set up along 
          with Allaah another ilaah (god); but they will come to know”
[al-Hijr 
          15:94-96]  
The Christians are among these mushrikeen 
          because they worship the Messiah and his mother, and they worship the 
          cross. So do not pay any attention to them or their mockery; turn away 
          from them and do not enter into debate with them, lest they make you 
          confused with their specious arguments. If you can change schools and 
          move to a school where you will not be exposed to this trouble, then 
          do so.
 The Mormon sect appears to be Christian 
          because they mention their book, which is the Gospel (New Testament), 
          and they say that if Islam were like this, i.e., opposing their religion, 
          it would have refuted their book. This is ignorance and confusion on 
          their part, for Islam does not refute the Injeel which Allaah revealed 
          to ‘Eesa; in fact the Qur’aan confirms it and the Books that came before 
          it. But Islam refutes the religion of the Christians who have taken 
          the Messiah and his mother as gods instead of Allaah, and Islam refutes 
          the distorted Gospels which are in the Christians’ hands. Allaah says, 
          after mentioning the Tawraat  (Torah) and Injeel (Gospel): 
“And 
          We have sent down to you (O Muhammad) the Book (this Qur’aan) in truth, 
          confirming the Scripture that came before it” 
[al-Maa’idah 5:48] 
          
i.e., the Qur’aan confirms the Books which came before 
          it, such as the Tawraat and Injeel.
The Messiah has disowned these mushrik 
          Christians and their way, and he will disown them on the Day of Resurrection, 
          as Allaah says (interpretation of the meaning): 
“Surely, 
          they have disbelieved who say: ‘Allaah is the Messiah [‘Eesa (Jesus)], 
          son of Maryam (Mary).’ But the Messiah [‘Eesa (Jesus)] said: ‘O Children 
          of Israel! Worship Allaah, my Lord and your Lord.’” 
[al-Maa’idah 5:72]
“And 
          (remember) when Allaah will say (on the Day of Resurrection): ‘O ‘Eesa 
          (Jesus), son of Maryam (Mary)! Did you say unto men: ‘Worship me and 
          my mother as two gods besides Allaah?’  He will say: ‘Glory be 
          to You! It was not for me to say what I had no right (to say). Had I 
          said such a thing, You would surely have known it. You know what is 
          in my inner‑self though I do not know what is in Yours; truly, 
          You, only You, are the All‑Knower of all that is hidden (and unseen). 
          
Never did I say to them aught except 
          what You (Allaah) did command me to say: “Worship Allaah, my Lord and 
          your Lord.” And I was a witness over them while I dwelt amongst them, 
          but when You took me up, You were the Watcher over them; and You are 
          a Witness to all things.’”
[al-Maa’idah 116-117]
We ask Allaah to make you 
          steadfast in Islam and to suffice you against the evil people. May Allaah 
          bless our Prophet Muhammad and his family and companions, and grant 
          them peace.