Irresponsible online seller-Paytm and its worst support to customers

I don’t trust Paytm , they have delivered a second hand mobile as a brand new one. The customer care and support is very bad.
Here is my experience.

I have purchased one micromax mobile through paytm from ICE tree collection in July,2015.

I got some problem with that mobile recently, so went to nearest Micromax care, there I got surprised to know that the IMEI of the mobile which I’m using has been activated in November,2014 i.e almost 9 months before the purchase of the mobile, since its been more than one year of activation of IMEI micromax care said that the mobile
is not covered under warranty, but it is only five(5) months from date of purchase.

I contacted paytm, they requested some letter from micromax care and images of invoice and mobile. I have sent all what they requested they took 3-4 days time and replied that I need to contact the seller and asked me to refer the invoice for seller details.
when I refered the seller details on invoice, I found one address referring delhi and one contact number. As it will take more time for going to delhi or sending complaint letter to delhi, I telephoned to the contact number, to my surprise it is Paytm’s customer care number.

Isn’t it the responsibility of Paytm to check the vendors/sellers before displaying their products online through paytm website?

For sometime lets think that unfortunately the seller/vendor which paytm trusted has cheated the customer

when the customer who has been cheated by seller contacts paytm, isn’t it the responsibility of paytm to give proper customer support and see the issue got resolved and never reoccur.

How can I trust Paytm when I have been delivered an second hand mobile as brand new one and there is no proper customer support.