Not honoring the contract

I have a service plan with them. I got confirmation from them that my car is covered for one more service with them, in writing(email). I take my car in for service, they then refuse to give authorisation for the service to the service station. I have a fully paid-up policy(service plan). The service they are refusing to give authorisation for is an R11000 service. They also have a different car loaded on my policy profile than what I own, but if they use my policy number to review my policy details, they can see the car I actually own. I have tried for 3 days to make some headway, but I get to put on hold or are told they will call me back, which they never do.