Marees Enterprises - Advance paid no service or money paid back

I have a Rachold Eterno * storage water heater of ** liters capacity. Lately, it stopped working & kept on breaking the electrical circuit whenever switched on. 

On *th May I started finding service people near me in Google search. After dialing a few phone numbers from Google search. I got a callback from Mr. Ravi of Marees Enterprises.

I shared with him the address & details of Gyser via Whatsapp. His staff Mr. Kannan sent to my home to attend to the issue. He dismantled & checked the product. He gave a bill of Rs. **** for replacing the coil, & thermostat set after an oral confirmation.

I couldn't arrive at the service/product cost at first so I reluctantly paid an advance of Rs. ****/- through Google Pay to Mr. Ravi. 

After checking the product's original price & spares cost online I was surprised. Because they are charging *x of quotes that I got subsequently.

I did visit a few local shops as well. It is clear that Ravi & Kannan were trying to charge me more than the product's original price. 

According to their split up, the coil alone costs Rs. ****/- but the market price is in the range of Rs.**** to Rs. ****. 

Having known their intention I asked to cancel their service & issue a refund. The duo is claiming that they have already purchased the coil & other spare products, at any cost, I'm bound to pay Rs. **** for just dismantling the geyser.
 
I have requested service cancellation & advance refund the immediate next day. It's been a week I'm hearing different stories & no sign of getting my money back. Finally, Mr. Ravi calms that he has got support from a political background & his uncle is an MLA.

I've wasted several hours trying to reach them & following them but no luck. I'm sure they are overcharging several other customers the same way.

I couldn't find their business online only a phone number is showing up. Their bill has no company registration number or GST number. I've WhatsApp chat & Google Pay confirmation to serve as evidence from my side.