Disappointing service

Had my vehicle serviced on the 10th Nov. No issues with the service it self but the following day I saw that the bonnet had a dent that was not there when I took it in. I was phoned to collect my vehicle around 3pm and was in a hurry to get back to work so I didn't see the damage immediately. They insist that it was not them and even tried telling me someone might have tried to break into the car. There are no scratch marks on the outside and it is clear that the damage was done from the inside - like someone closing the bonnet on something hard. They even tried telling me that I might have had someone open the bonnet after the service - why would I do this if the vehicle was just serviced? I also tried asking them if they can assist with the process of getting it fixed as I am not sure what to do and they clearly aren't going to accept responsibility. I have not received anymore feedback after I asked that. My mail was sent on the 19th Nov and still nothing. They even sent me photo proof that my vehicle was 100% when I took it in. No proof that it was received in the same order and I didn't to check as it has never before been necessary. I have been a client of this branch for a couple of years now and always received excellent service. Very disappointed in the way this was handled.