BAD SERVICE FROM FORD CERNTURION

I took my car for service on the 16/07/2019 a week later (24/07/2019) my car show a pop up that says" engine service needed now" I then went back the following day to tell them wants happening with the car, they told me that I need to pay for them to test the car on what is wrong with it. when I ask but you did the service last week why did you not check the car they said" they do not test the car" and they will not test it for me if I do not pay it. how do you do a 120000km service without testing what is wrong. i will not recommend any1 to go there because there service I got was very bad.. my name is Phindile Mkhize