What should i do cousins boyfriend is saying i hit his car?

during spring break i went over to my cousins boyfriends house. he claims that i backed in his car. which i didnt. his mom called my uncles house looking for me when i called her back she said she was going to get a lawyer. it has been over 3 months almost 4 we leave in oklahoma.her son is 22 and has put his car in the ditch. he is saying i caused over 2000 dollars for damages which i didnt do. how can he file a case without any proof and how can i really prove i didnt do anything.