VAJRA COOL LAND - AC Installation Cheated by fake Voltas technician

I have called Voltas customer care number *********** on **April**** and booked for AC installation to my Madurai house address. Next day I got a call from local Voltas technician for installation process.
They have installed the AC (**April****) and has taken unnecessary charges (Rs.****) and also not shared the invoice with me. I have called them multiple times, However they are just giving a false assurance that I will get the bill online through 'WhatsApp' and has not shared anything till now.

After installation, From day * AC is not working properly. Got error messages and Ice forming issues. Have called them multiple times and I didn't get any proper response.

Almost a month I decided to call another local AC technician and he checked and found the GAS was not closed properly.
And he called the Voltas technician to check the GAS details and came to know they are fake Voltas technician. I directly came to their office but i didn't get any proper response from them. Kindly help for Refund ...