Poor service and implementation of the service plan.

My Mom(T.E Kunene) is a pensioner and today she took her car for 100 000 service at Vereeniging Mercedes and was assisted Chanerz Fernez ( excuses the spelling). The millage was 205 km over and she was told she has to pay for the service. She refused because it's the 100 000 km service which falls under the service plan. When she called to book it in last week she asked about the above they said it will be covered. When they called to collect the car, they changed saying she needs to pay. Also my complaint is that it is the service for 100 000 so why is not included. Also she is a pensioner no one explained what they are saying now.