Voltas — Got scammed by Service from voltas

Address:

ahmedabad

I called voltas for repair because my AC was not auto-cutting power.
After call, they send someone to my home for AC check and they told me they were from voltas they took off the motherboard and told me to change so we agreed.
after 2 days they came with the same motherboard, fitted it and cutoff worked and charged 7000 rs. and told me it have a 3-month warranty.
in week my cutoff again stopped so I called them and they told coming and no one came. and afterward, he blocked me.
I called voltas cust-care regarding this issue and voltas told me we have no complaint from your side and we haven't sent anyone to your home, and I have proof and call recording that I've called on official voltas number given backside of remote-control, and now who is responsible for my 7000 loss?
I am stressed because of this incident and plz suggest what actions I take, I've voltas bill as well given by that serviceman.