Neurogize Returned the pkg they sent me & claims they sent me 2 boxes. Won't refund money. They only sent 1 envelope. San Diego, California

I ordered a sample. Payed with debit card for shipping. They took money from debit card & shipped sample. After I rec'd sample they deducted $74.98 & shipped me more. I called neurogize & cancelled order but I also did not order anything but a sample. They told me they shipped product & gave me a return # to put on pkg. so when I rec'd I sent the envelope back. I never opened the envelope so I have no idea what was in it. They claim they rec'd the envelope back, gave a partial refund & said they shipped 2 boxes, which I never rec'd nothing but one padded envelope. They owe me $39.99 & refuse to refund my money. They claim I stil have another box which is not so.