Damaged my car

I went to PG glass East London for glass fitting on16th January 2018. On arrival pre inspection was done. Around 15:52 they text me saying they are done. I went there to fetch my car. I paid went to the car to drive away. I noticed my rear mirror is stiff. I went outside to check. I noticed the holder is broken. When I complained they say it was broken before fitting. White lie,they broke it. I send them images of damages nothing is done until now. Even head office knows about this matter.