Service horror

I purchased a 2019 Citroën c3, to me it was advertised as 2020 model. I purched the car in September 2020. I went for my first service on the 07 December 2021. I was advised that I can not service my car because I have skipped the first service in December 2020. The service plan is 5 years, that means I have forfeited 12months/15000km of service. Please correct this error and allow me to service my car for first service and 15000km.