a learner passed but following year was told faile

My cousin was doing grade 11 2015 he was told he passed the grade December by means of a progress report.when he came to register for grade 12 2016 he was told he failed.but the marks shows he passed.a specific teacher dislike him and has been having bad attitude towards him for 3years.please help..my cousin is rotting in grade 11 he is going to be repeating it for 3 years now.