Item not as described

[NK346f2849X127d8bca260]

I bought a school jumper described as Trutex Gold , but although it is a Trutex one it is not the same as the one i bought from school shop far inferior quality. Also when you measure the jumper it is 2 inches smaller than the label says so is too small.
I bought it on a BIN from an ebay shop, they say no returns unless faulty or damaged.
Is there anything i can do?

It's faulty. Return it.

Yep it's 'not as described' in style/brand and size, therefore you are well within your rights to return it.

What should i say in my message to them?

NK, however do you remember your name?