Unauthorised service done on my vehicle

My service plan provider booked my car in for a service at Bosch car service auto electric Strand. Booked the car in at 8am 15th of March 2021. I had to phone them at 4pm because they never made contact with me the whole day regarding my car. After being told that there are parts that need to be replaced that is not covered by my service plan, I requested my car back, only to be told the service has already been done with out my permission and I will not receive my car back until I make payment.