i got in a car accident?

[Brian]

i was at a stop light waiting for green arrow to flash so ican turn left allowing me to turn left withouth yielding( no cars behind me or infront of me to turn left too so i wasnt trying to race no light ext) . on oppisite side person was at stop to waiting for her green light to drive foward green arrow flashes meaning i can turn to left i go other driver drives foward we crash policeman saying its my fault because i was turning i should of yielded even tho i had right of way the other person states her light was green. my moms insurance provider will not cover me possibly if i go to court how would i win the case when i would have to face other insurance provider and i wasnt at fault .