Hi I bought a yorkie T-Cup puppy 4 months ago but he does not look like my other T-cup Yorkie the more he grows up. The hair is straight and the body is longer. Is it possible he is not a purebred? I have paid for 1500 dollars and wonder why.

Google image Yorkie teacup puppies, You will see different cosmetics and body structure depending on the bloodlines they were bred from,, Yorkies look similar but are not always identical either

your dog could be a chorkie which is is designer dog breed mix of full yorkie and full chihuahua. I have a chorkie that looks just like pure bred yorkie but his body is longer like chihuahua. everyone still thinks he is a yorkie

I can't help you because I don't know anything about T cup Yorkie