Worst service from Mercedes

Bad customer service from the service department from Mercedes Benz Eastgate/Bedford. I bought a used Vito in December 2019 with 37000km on the clock. I checked with Mercedes if everything is still in order with the car in terms of service plan and warranty and I was told all is good. Checked the next service on the car and it said B service is only due in 75000km. Fast forward, the car reached 75000km for B service, I took it in and they tell me the service plan has elapsed because the car was not serviced at 40000km and the car never said anything about a service at 40000km. I took the car in at 7am after I told the service advisor that I use the car for business so I need it back before end of day. He only called me at 16:35 to tell me all of these and disappeared. I tried calling the following day with no luck, fast forward to 6 days later, I walk into the dealership and the service advisor is not there and my car has not been allocated to any other service advisor. I talk to one of the service advisers who told me stories that maybe the car was tempered with so it can miss the service. How could I temper with my car to miss a service that I don’t have to pay for and what would I gain from my car missing a service? I’m completely not happy with this and I just want my car back so it can go back to work. I agreed I will pay for the service just so I can have it back working, but I still haven’t received any call from them and today marks the 7th day since my car has been in for service. I don’t even think aeroplanes take this long in for service. Their service is appalling to say the least.