Mercedes Maintenance Plan

We bought a CLA Mercedes 2017 model and it had 24000 km on the clock. Since it is our spare vehicle we do not often use it. We live in the middle of the Karoo and hence do not have quick access to service centre's and have to travel 500km to the nearest service centre. Our car is 450 days over its second service but we travelled infrequently. When we went to Roli- Mecedes in Somerset West today they are stating we need a new service plan as the days due to our service is too much. This is as per Mercedes Benz rules apparently. I have to pay almist R7000 for the service today. I am extremely unhappy as we have seem to have lost our entire Mercedes Service plan. What would happen if we would have been living abroad and the car was parked in a garage??? I have had many Mercedez under Maintenance plans and this is a first for me that a car MUST have a yearly service irrespective of mileage. In the past mileage was the main factor. Who can we take this up with pls as I do not believe it is an ethical service plan where it can be cancelled even after I have now paid the R7000 fir Service B.