Godrej Appliances — misguide from customer care and also service center person and they charge me a lump sum amount without intimate me

Address:

1/2A, LAXMINARAYAN MOTILAL ROAD, JAIRAMPUR POST OFFICE, Kolkata, West Bengal, 700061

I am a senior citizen (80 yrs.) retired govt. Employee. Two years before my son bought me an ac of 'godrej co'. It is truly very fine machine since bought. Recently due to the extension of my house my son contracted with the customer care for shifting the ac from one outside wall to other side of the same room. Customer care told my son that the shifting charge is around rs. 1900/- and also booked our request. The next day local service center office telephone me for this purpose. I agreed, they came and done their job. After finishing the shifting process they handover me a kacha bill (gst free) of around rs. 9600/-. I became shocked and wanted to know bill details and demanded paka bill (with gst). They forced me not to give the bill and if the bill is generate the amount will be increase. When i go through the bill i became shocked to see the bill.
Sir my ac is only two years old and it is still in good condition but they changed most of the item intentionally and made the bill without any intimation. Now i am in great problem to make the payment. Though i have given them a cheque of dated 05/06/2019 of total amount but it will be a very difficult mount of june for me to carry on my expense. Please look into the matter and punish them. So, that they will not be able to cheat any person like me.