Since I was 15-16, my grandfather has been making sexual advancements towards me. He propositioned oral sex with me before (though my grandmother came home then and it didnt get far)

Now 8 years later he's starting up again. He started walking around without clothes, started flashing me on purpose and even offered to buy me a $200 phone in exchange for oral sex. (He wrote it down on paper and handed me his "offer" saying it was a fantasy of his to do this with me)

I told my grandmother who confronted him and he denied, yelled at me saying i was a manipulator and liar, asked for proof and said I was destroying the family.

I have no clue where to turn and my grandma is equally as lost because at this point its my word against his and because he threw the evidence away i have nothing to back my side up. My grandma believes me as much as she can since shes caught him nude before but she doesnt want to believe hes like this.

So as the title states, is this abuse? And if so what should i do?