What has happened so far?
If you tried to start a return for the item you bought and you chose the reason wrong size/doesn't fit, then a private seller would be able to refuse the return and the case would close.
If the item was too big and damaged, then you did need to choose 'item damaged' as the reason. No seller can refuse a return for a damaged item.
If this is what has happened so far, then you can use the link provided by @plum993 and ask Customer Services if they can possibly open a new case for you. Usually, you only get one chance to open a case.
"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)