Can't help after appointment was made

Made an appointment for a service. On arrival at 7:20 they tell me that I can only book the car in at 7:45. After they told me when I made the appointment that I can bring the car any time between 7 and 8:30. According to the person at the garage they tried to phone me but I don't have any miss calls or messages on my phone. So I was the only customer in the office and the person just said I can't help all the people at the same time that's why you should stay with your time which I never got. The person did not even try to help me.