All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Being undutiful to one’s parents is one of the most abominable and forbidden sins as we clarified in Fataawa 84942 and 87856.
However, if you had been undutiful to your mother before becoming pubescent, then you were not sinful because you were not then held accountable [as you had not yet reached the age of puberty] and your mother should know this, so she should not hold you into accountable for what you had done before you became pubescent. There is no doubt that her conduct and her refusing to forgive you is not a proper conduct because it is more appropriate for her to accept your apology and help you obey her and be dutiful to her.
As far as you are concerned, you did well by endeavoring to seek your mother’s forgiveness, and we ask Allaah to facilitate this for you. We advise you to supplicate Allaah as much as possible in order to soften her heart and make her accept your apology and forgive you, as Allaah is The All-Hearer and He answers the supplication of the one who supplicates Him.
Hence, you should be kind and soft with her in order to render her affectionate with you as in principle a mother is merciful to her children. Also, you may seek the help of some of her female friends who may influence her.
If she does not respond, you should supplicate Allaah on her behalf as much as possible and ask Him to forgive her, and you should also do other kinds of acts of being kind to her while she is alive and after her death hoping that Allaah would make her pleased with you.
For more benefit on how to be kind and dutiful to the parents in their life and after their death, please refer to Fataawa 82254 and 83233.
Allaah Knows best.