There are not many circumstances where a seller can close a case where you have requested a return.
How long after receiving the item did you open the case?
You only have 30 days.
What specific reason did you give for wanting a return?
Unless it was a 'change of mind' reason (I no longer want this/don't like it) the seller would have to accept the return.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)