Disgusting customer service

Sent in my car for a service on Friday. The car came back slacking and making strange noises hadn’t make before. So I sent it back on Tuesday for them to only tell at 2pm that they didn’t know what the issue was and were only going to run diagnostics. I still don’t have the car with me and they’re still running “tests” I’ve missed two crucial days at work and they are so nonchalant about it and they’re acting like they’re doing me a favour! I’m absolutely appalled!