Grad student in need- surprise health insurance bill appears 6 months after visit

I had a suspicious mole removed last September and even made sure to call my insurance company beforehand to see what the cost would be to me. I was told there was no deductible and that I wouldn’t be billed for anything. Lo and behold, six months after the visit to the dermatologist, I get a bill for $415. I’m a grad student getting my Masters to teach high school science and have very little money to my name at this point. I would love a little extra help!