First, collect all your documentation. If you haven't yet, keep records of dates, names and even times of contact.
Next send them a "certified return reciept requested" letter that asks them to respond within a certain timeline.
In the letter include sentences like "I have been advised to keep records of all transactions and communication from this point forward." If you aren't great at writing, find someone who is, and can write very formally.
You will give the impression that you are preparing to sue them and are already talking to an attorney. If they are a 2 bit scammer, they won't care. But if they are simply unscrupulous businessmen/women, they may refund your money just to make you go away.
So the letter may look like this:
"Dear Sir or Madam;
On (enter date) I purchased (enter item). The item arrived in defective condition. I have followed the RMA procedure outlined by (insert name of person) and sent emails on (enter dates). Thus far, all communication from me has been illegally ignored by your company.
I have been advised from this point forward to document all communication with you in a legally verifiable manner to resolve this issue.
You are formally requested to provide accurate RMA instructions, to replace the defective merchandise or refund as necessary within
30 days of reciept of this letter. Failure to do so could result in claims of further damages, including punative damages if it is perceived your company is acting in bad faith.
Thank you for your time and attention to this matter. I wish to resolve this without further legal involvement, and insist you immediately address the defective merchandise sent by your company.
Sincerely, etc. "
Send the letter typed, on high quality paper, with a printed envelope.
Believe it or not, most companies I've done this to
immediately respond and take care of the issue. If they don't, you're likely dealing with scammers that don't care, and you might as well look at trying to prosecute if possible.
As mentioned by BenF, contact BBB and make a report ASAP. Also c627627 suggestion.
Good Luck, and dont' forget to update us WITH NAMES.