His parents, if those are his parents, are purebred.
My first impression is the really young picture looks purebred, the older ones don't. If that's the same dog I don't know what to say. I've seen markings change as dogs age but I've never seen a puppy with a full blanket change to a puppy with no blanket to speak of in what... weeks? Is it because his guard hairs are all missing/shaved out?
You're from Pakistan, right? Don't you have a registry there that keeps track of purebred dogs?
It comes down to this:
If there is no registry that has kept track of his lineage, you'll never really know if he is purebred. When he grows up, it'll be easier to tell. Right now all we can say is that his parents look absolutely pure and he looks like a mutt.
Maybe by some freak accident his mother was bred by the purebred dog and by a mutt as well? I know in some animals that can lead to different sires for different offspring in the same litter.
If those are his parents, well, then he is a purebred, and most of us are wrong, end of story.
Can you prove those are his parents?