6 yr service plan actually only 5 and a 1/2 years?

Bought a new Kizashi December 2013. They come with a 6 year/90000Km service plan. Booked the car for it's first service in Febuary 2015, I was informed Suzuki SA cancelled the service on the system due the fact that it's overdue. Understandable, seeing that the 12 month service interval would've required the first service in December 2014. However, the service was cancelled because the first service was due in May 2014. I was told that Suzuki Menlyn had pre-registered the vehicle in May 2013, and that my service plan runs from that date, not from December 2013. Nowhere on any of the contracts or documentation I signed, or at any time during the sale were I informed of this fact. I've mailed Haman Boola from Suzuki SA and Wessel from Suzuki Menlyn to explain to me how it's possible for me to only have a 5 and a half year service plan instead of the advertised 6 year service plan. The car is currently on 18800km and was serviced three months ago, and now I'm told it needs to go for it's 30000km/2 year service or I'll be required to pay for it myself, even though according to me it should only need it's next service in December 2015. How can this be considered legal or acceptable?