Im getting bullied because my dad died ? help 10 point best answer?

Hi im 15 and in the Uk and when i was in year 5 my dad suddenly died i was so upset but i carried on with life and in year 8 i was at my friends and she said that another girl that i used to be close to in primary then drifted had said i pretended to be upset when my dad died because if i was upset i wouldnt have gone to school the next day (he died on a sunday) but i felt i had to keepm mind focused and anyway i didnt go to lessons i helped out with the playgroup but then in year 9 i really fell out with my closest friends and they started bullying me and at first it was about me and the way i looked and my personality but then they started saying oh jade hasnt your bus come yet why dont you get your DAD to pick you up and have you got your dad a fathers day card yet hahahaha but i carried on for ages and i ended up moving school but i didnt tell my mum what they was saying and she didnt know they mentioned my dad should i tell her and how do i deal with the loss x