Nissan - not returned CNG parts from service centre and now they lost it nd now

Writing this with a lot of disappointment, anger and frustration.

I gave my car Nissan Terrano to Etco Nissan service centre in jogeswari Ram mandir area in Mumbai on **/**/** for engine work, got the delivery on **/**/**. Paid a huge amount of *.** Lakh for the engine work to the service centre. My car was with CNG Fittings and some parts of the CNG kit was removed for servicing purpose, completely understandable. Unfortunately some parts of CNG kit were not returned with the car while delivering in June ****. I being a lay man never knew that CNG parts has to be REMOVED for servicing, nor i was informed that parts has been removed. I was just informed that CNG kit will be disconnected. I assumed that things can be disconnected even without removing them, cause it is possible in many machines or electric parts.

Now after * months in dec **** i want to reinstall the CNG kit, and now it was shown to me through the installing people that some parts from the CNG kit are missing and were not returned to me from service centre itself. On asking the service centre for the missing CNG parts i got a shocking reply that they have lost it or gave it in scrap due to the long time period. Now I am blamed that it's MY fault for NOT asking my parts while taking the delivery of my car, now its MY fault that i was unaware about the car CNG mechanism, and it was MY responsibility to claim any missing part from the service centre. This is highly disappointing i feel.

From my point of view this is completely unethical to blame it on a lay man to have knowledge of car mechanism. If some part is removed from the car and its in working condition and does not belong to the service Centre then it should have been returned to the respective owner by default. Why should owner have to ask or beg for it?? Isn't it service centre's duty to return parts of the car to the owner?? Does Owner has to dig inside the machine go through it and ask for any missing part? Seriously does this sound right??

Now I am claiming for my missing CNG parts which are "CNG Wiring", "Mapsensor" and "Injector" of the company "Automoto", but the Service centre is completely rejecting my request that nothing can be done now and I will only have to bare the cost of the parts I lost. I want a solution for this where Etco nissan service centre is accepting the mistake but they are not ready to pay for the parts they have not returned.