Service plan dilemma

Dealing with Nissan has been the worst experience of my car ownership life. I took my car in at Nissan Northcliff to change my battery back in April 2017. In picking up my car I realised that they serviced and stamped my service manual for 30 000km, when in actual my car was sitting at 18 000km. I told service assist that that was incorrect and that I didn’t bring my car in for service as this was a warranty problem. He amended his mistake and put the correct 18 000km and signed next to it. Little did I know that he had to correct the number on the system and not only manually. Today my car is due for 30 000km service I went through the normal process of booking the service but however they are saying according to their systems its due for 45 000km. This is due to the fact the service assistant did not correct the service interval on the system from 30 000km to 18 000km as he did in my service manual. Who is at fault? Is it me for trusting and not questioning Nissan quality of service. Because: 1. Nissan incorrectly serviced my car for 30 000km when it was only 18 000km. 2. They corrected it on my handbook but failed to correct it on their system which they should have done the day I left. As a customer is it my duty to also go and check their systems if all is correct and in order? If you sum it up there are 3 different numbers. a. 29 000km registered service on their internal database. b. 18 000km corrected and signed in my service manual. c. My car speedometer is currently sitting at 31 569km however they want to service me for 45 000km. If my math is correct 31 569 km is closer to 30 000km than 45 000km. With all the above stated, where there is proof of all this, I would think Nissan would have the common sense to notice that the error is on their side. I purchased a Nissan when I could easily have gone for any other car brand because I had the impression they had a superior service standard. Was I incorrect? Yes I will agree my car is still under its service plan and to many the problem will be solved whether its 30 000km or 45 000km however it is unfair as I paid for all service intervals, I do not want to lose any of them due to their own errors. I am no expert at the consumer protection act however if you pay for something you should receive it. I do not want to take the route of contacting the CPA to get this addressed, @Nissansouthafrica please can you investigate and rectify this unfortunate mistake that was done by the people you hired at Nissan Northcliff or further escalation to CPA will be taken.