Dishonest dealings

We took our car to a mechanic to find the reason the car switches of whilst driving. They asked this company to test the electrical stuff. They responded that we need a part replaced, which was purchased by the mechanic and they were going to replace it.<br> <br> Two weeks later, the car was returned to us saying we must pay cash to get the car. There was additional part ordered and replaced with private people doing the programming. I asked for an invoice before I pay and was told I was difficult. The invoice then given to me had no details. Once I got the invoice that gave the details of what we paid for we were:<br> Paying twice for one part, Paying for a part we did not authorized. We also paid for replacing the first part that was bought by the mechanic and it was NEVER replaced. He told me that Opel did not want to program the car as their equipment was not working but Opel told me that they tested the car and told him nothing was wrong. Very dishonest, stay away. I will get my money back from the Small Claims Court.