MSOffice 365 pre installed on Lenovo Laptop instead of MS Office 2019

They lied. Send it back for a refund. One time Office 2019 Home and Student costs US$150 (I don't know the equivalent in India) which is a significant fraction of the price of a PC purchase. If they said it was supposed to be there but it wasn't, and they won't provide it, you've been ripped off. Return it!

Take a look at the original order for the computer. Does it explicitly say it comes with Office 2019? Do you have the original ad for the computer? Take a close look at it.

Or did you pay separately, extra for Office 2019?

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Did it come with separate Product Key card in the box?

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Start one of the Office applications. Go to File menu > Account command.  On the pane displayed, does it show more than one copy of Office installed, something like this:

except that both need activation?

I purchased from Amazon India S 540 series laptop with pre-installed Windows 10 and Office 2019. When i tried activating Office 2019, it could not be done. I got a screen indicating that Office 365 is loaded and i had to subscribe and pay for it. When i took up this matter with Amazon, they said they are sorry about this but cannot help me resolve this issue. 

Can i get some guidiance on how to proceed in this matter. Thanks in advance.

Did the laptop maker state specifically that it included a pre-installed 'free' version of Office? Presumably an HP laptop?

If that is the case you have to start Office in order to create the MS Account as per the PC makers instructions

As part of a deal with Microsoft manufactures install a free trial version of Office 365.  Some manufacturers also add another version of Office, it will usually be  Office Home and Student.  Unless you want to use the trial version of Office 365 you need to uninstall it.  See this for preinstalled Office.  Click on the links for further info