Bad service

took my Ford Focus in as a walk in on the 9th of January at the Lazaurus Ford in centurion John voster because the car was jerking and the engine light was on, the attended to the car on the 14th and advised that it’s the engine coils needs replacement, the replaced them and received the car on the 15th in the morning drove it to work to my surprise the car still had the exact issue I took it in for. I drove the car back to Ford the following week the came back after I made follow ups and the said the is nothing wrong with the car. An electric diagnostic was done and nothing came up, I told the technician that he must find out what is the problem with the car. They have since parked it at Ford and I have not heard anything from them.