Lindsay saker or Avis

Hi Peter, I have a query on my service plan, since I bought my car from Avis( and is under Optimum Service or Avis) I have been servicing my car at Lindsay Saker Midrand, to my surprise when I took my car for 75k km's service they have informed me that the car is coming for 90k km's service, im surprised of how did the car jump 75000 to 90000 where as per actual km’s on the clock is 78000 km''s, the new lady service advisor informed me that the previous service advisor is the one mix up things, I have tried to contact Avis with no luck, they took me from pillar to post, no one want to take responsibility, Lindsay saker and Avis( or Optimum).