Poor client service - overbooked and poor time management

Last week I booked my car in to have the heater fixed. I was informed it would take half a day. Long story short they only quoted me that afternoon and did not look at the car until the next day. (Sat) On Sat at just before 1 pm and told me the pipe was corroded (surely this would have been noticed when working on the car) and they need a new one so I will only get my car on Tuesday as Monday was a holiday. I informed them upon booking the car in and again on Friday afternoon that I was going away on Monday. I had to rent a car for my holiday and incurred an extra expense. When I told the mechanic this, he said **** happens. I asked them to contribute towards the rental and they refused.