How To login a register a consumer complaint.

I had face a issue with the Onlineshopping company, I/ve purchase one of the onlineshopping site, & everything went fine, i recieved the my order within 2days, i paid for it, after that i came to know that item had damage/defect, on the spot i saw i register a complaint in their site & after that i had to wait for 2days for call back(poor support) from them & i try to with telephone but they said one of the person will contact you asap, & finaly i recieved call from them & i share my issue with them, they told they the same item on stock & will replace it within 2days , but i wait till as per rules for 7days & call back them because of no response, that time they told the stock is not available if you wait for 2moredays you'll recieve it ! but still no more response from their side, so i call back again still they told still it the stock not yet came kindly wait agian & then i told i dont want that & replace with other item & i given my new item order and they told they stock & you will recieve it by 1day, but still they didnt delivery & when i call back they told agian you'll recieve by tonight , but still not yet ! so how could i register complaint against them, & will i recieve justices on it ! kindly tell me the procedure on it !