This is bullying. No question. When my youngest daughter went up to secondary school she was so unfortunate as to have in her class a girl who I had taught top Juniors the year before (a job I took because the school I was in closed and I needed a year to find my feet in my natural home, Secondary). This girl gathered a cohort and dripped poison about me to my No. 2 for almost a year (What a horrible person your mum is, based on my having had to discipline said child.......... It is only now (she is in her mid-30's) that the damage has been cleared - daughter also now works in Education and understands what goes on. The perpetrator was unearthed last year and was truly repentant, so that helped.
No, you are not OTT - speak to school, please.