Money making scheme

I took my car for service on the 1st of August 2019 and a few things were changed. After a week then an engine light went on I went to Ford to ask what was happening they told me I should pay R850 for my car to be diagnosed. I wasn’t happy with popping up money when my car had just been serviced and I thought to myself that they should have picked up if something was wrong when they were servicing the car I mean that’s why we take our cars for service right? I am not happy with the service I get from Ford. After the service Zelda promised to email me the invoice as I paid extra for replacements but I never received it until I went there and as I was asking she rolled her eyes as if I’m asking her something that is ridiculous. The engine light is back on now and it’s frustrating me cause u can’t be popping out money for everything. I once purchased a battery and they charged me R750 for Labour which was ridiculous.when I was still with Toyota I never experienced this that’s why I feel that I should talk about it and I’m definitely not buying my next car from Ford.