Skoda Kodiaq Develops Engine Fault Right After $1,393 Major Maintenance

I took my 2021 Skoda Kodiaq to the Çorum Skoda Ahlatcı authorized service center on April 20, 2026, for major maintenance at 120,000 km. Even though the warranty had already expired, I specifically chose the authorized service center to avoid problems down the road, and I paid approximately $1,393 for the timing belt, V-belt, spark plugs, transmission fluid, and regular oil maintenance.
On the day I picked up my vehicle from the service center, I noticed that fuel consumption had increased noticeably and that acceleration had dropped. The vehicle also gave a start-stop warning and the check-engine light came on. Once I had time available, I scheduled another appointment and took it back to the same service center. Before my vehicle was even put on the lift, I was told there couldn't possibly be a problem related to the work that had been done. Afterward, following an inspection, I was told that carbon-buildup cleaning would be needed, which would cost around $300, and that if this didn't resolve the issue, the coils would need to be replaced at a cost of around $257.
Having my vehicle — which had no warning lights on and no issues with acceleration or fuel consumption before the maintenance — returned to me in this condition after major maintenance, and then being told, before the vehicle was even examined, that no connection could be made between the problem and the work performed, left me seriously disappointed. The reason I paid extra to go to the authorized service center was so I wouldn't have headaches and could drive with confidence, but right now I'm suffering both financially and emotionally.
I am requesting that Skoda and the Çorum Ahlatcı authorized service center thoroughly investigate the possible connection between these malfunctions that emerged after the maintenance and the work that was performed, identify and resolve the problem without charging any additional fees, and provide me with a clear, written response regarding the grievance I've experienced.