Unprofessional and unpleasant service

A petrol attendant was negligent with my car and it damaged parts of my engen. After a very unpleasant meeting with the man in question and his superior they assumed responsibility. I was told to fix the car and send them an invoice. I asked the superior to put that agreement/commitment in writtting and she refused saying this is the way they work and there is no written confirmation that she will do for me, I should take her word for it. I cannot give the mechanic a go ahead to work on the car without proper commitment from Engen. I have been without a car for 9 days. I will now be liable for storage fees as my car has exceeded the number of days it can be there. My business had to be put on hold because my car is my main resource. I called the call Centre but nothing has been done yet.