Bullies and poor customer care services

I took my car to Dal panel beaters in Groblersdal last year as suggested by my insurance company. During their process of fixing it they mistakenly damaged my windscreen and now they claim it came like that, yet there is nothing supporting that. The accident report, assessment picture and the quotation they made does not even have windscreen. When I try to talk to them to resolve this issue they are threatening me that I should not even say a thing otherwise my car will be there the whole of 2023. They are now bullying me to take responsibility and pay so that they can fix it.