LG AC - Lg ac service

Lg ac faulty installation
Purchased through lg dealers in lucknow at family bazaar and installation done by themselves for which we paid charges for it and no receipt given for it. We thought it was an lg person.
One of the copper pipes connected to outdoor box was bent and we came to know about it at the time of cleaning recently by one of lg service persons due to which cooling is less.
Now the customer service and it's representative say that installation process was out sourced so we are not responsible for it. How come we will know this installation person was not from lg as he was sent by the lg ac sales people only.
Kindly do the needful as I feel now the worst service of lg and worst customer care service and there one of the representatives Mr. Gyanendra misbehaving on telephonic call. Talking very rudely not having any solution and making me responsible for everything as if I have done a big mistake by purchasing lg product.