您在这件事的权益中主要体现在您与修车行的书面合约中，但是听上去您好像没有任何的合约。您可以尝试以书面的demand note来试图与该修车行来和解，并要回部分的款项，如果失败了，您可能就要通过起诉的方式来维护自己的权益了
Your rights are governed by the terms of your agreement. Since it appears you do not have a written agreement, you will need to prove the agreement with testimony from witnesses including yourself. You might start by sending a written demand for a reasonable settlement of a return of part of your payment. If that fails, you will have to sue.
