Bad Service at Kia Fountains

I took my car for service at the Kia Fountains in Thabo Sehume on the 19th August 2018 and a week later i started experiencing difficulties with the car loosing power when accellerating or the rev count dropping in the middle of the trip and as a result loosing power. I took the car back only to be told that if they could not pick up the problem when they serviced the car it cant be their fault. the service manager decided to go outside with me to inspect the car and told me that the problem is actually the electrical components of the car and not mechanical, and i would need to book for a diagnosis for which i will have to pay for them to see what is wrong with my car. i decided to take the car to another mechanic on Saturday 15 September, who informs me that the throttle was not properly cleaned and the air filter was not replaced and that is why the car was giving me problems.