He thinks his mother used witchcraft against him and they are on bad terms with one another

It should be noted, first
of all, that Allaah has enjoined you to respect your parents and to treat
them kindly in word and in deed, and He has forbidden you to treat them
badly or say to them “Uff” (a word of disrespect). 

Allaah says (interpretation
of the meaning): 

“And your Lord has
decreed that you worship none but Him. And that you be dutiful to your
parents. If one of them or both of them attain old age in your life, say not
to them a word of disrespect, nor shout at them but address them in terms of
honour”

[al-Isra’ 17:23]

It was narrated that Abu
Hurayrah (may Allaah be pleased with him) said: A man came to the Messenger
of Allaah (S) and said: Which of the people is most deserving of my good
companionship? He said: “Your mother.” He said: Then who? He said: “Then
your mother.” He said: Then who? He said: “Then your mother.” He said: Then
who? He said: “Then your father.” Narrated by al-Bukhaari (5626) and Muslim
(2548). 

Hence you must stop your
mistreatment and saying that she is insane, because that is not appropriate,
and you should treat her in a kind and loving manner, and do not disobey her
commands so long as there is no sin involved. It is not permissible for you
to shun her and stop talking to her. If she does that then try hard to
reconcile with her by speaking kindly and doing kind deeds to her. 

It should be noted,
secondly, that it is not permissible for you to accuse a specific person of
having bewitched you, so how about if the person you accuse is your mother?
By doing that, you are accusing her of committing a major sin that may reach
the level of kufr. It is not permissible for you to do this even if the one
whom you accuse is a stranger to you, so how about if you are attributing
that reprehensible action to your mother with no proof or evidence? The
punishment for wronging others is severe, so how about one who wrongs his
own mother? 

Allaah says (interpretation
of the meaning): 

“And those who annoy
believing men and women undeservedly, they bear (on themselves) the crime of
slander and plain sin”

[al-Ahzaab 33:58]

Ibn Katheer (may Allaah
have mercy on him) said:  

The words “And those who
annoy believing men and women undeservedly” mean: by attributing to them
things of which they are innocent, that they have not done. 

“they bear (on
themselves) the crime of slander and plain sin” means, this is an
obvious lie, to say or narrate of the believing men and women things that
they did not do, by way of criticizing them. 

Tafseer Ibn Katheer,
6/480. 

It was narrated from Jaabir
ibn ‘Abd-Allaah that the Messenger of Allaah (S) said:  “Beware of
injustice, for injustice will be darkness on the Day of Resurrection.”
Narrated by Muslim (2578). 

Al-Nawawi (may Allaah have
mercy on him) said: 

Al-Qaadi said: It was said
that this means what it appears to mean, and it will be darkness for a
person who will not be able to find a way on the Day of Resurrection when
the light of the believers appears before them and on their right. And it
may be that darkness here refers to hardship, which is how they interpreted
the verse in which Allaah says (interpretation of the meaning): “Say (O
Muhammad صلى الله عليه وسلم): Who
rescues you from the darkness of the land and the sea” [al-An’aam 6:63],
i.e. hardships.  And it may be that it refers to punishment. 

Sharh Muslim
(16/134). 

It should be noted,
thirdly, that you may not have been bewitched, and it may all be illusions
and imagination. This happens to a lot of people, who believe that they have
been bewitched when that is not the case. So strive to obey your Lord by
performing obligatory and supererogatory duties, and strive to honour your
mother. Always read Qur’aan and try to recite the adhkaar for morning and
evening. These things, in sha Allaah, will protect you from evil and help
you to recover from your mental and psychological illnesses. 

And Allaah is the source of
strength.