If you get something which is not as described on the listing [different brand] then you go to the resolution centre [link below] and open a "not as described case" and the seller [if in UK] will send a label to return and refund. This is the only way to deal with it. There is no other realistic way to report this to ebay.
If several buyers open cases then eBay will probably ban them.
If the seller is abroad there is [or was] a way to deal with it through Paypal.
