Major service

I took my Audi A3 in Polokwane audi centre on the 04th of Nov 2022 for a Major service of which I paid 15 000 for, after two days the car engine light came on and it started loosing power. I took it back on the 11 of Nov 2022 and I was told that my car ignition coil needs to be replaced and it will cost me 10 000. How come it is only giving me trouble after they have worked on the vehicle and why these problem was not picked up during the service.