Depending on how long ago you purchased the bag you might still have the option of returning it to the original seller asking for a refund. If you paid via Paypal and are still within the required time-frame you can open a Paypal dispute stating that the item was not as described (ie, that is was described as a Coah bag, but is not). If it has been longer than the allotted time, you may still want to contact the seller and ask about returning the bag since it is a fake and selling fakes is against the law.
I had this happen with a fake Chanel quite some time ago. First, the bag wasn't shipped for quite some time, so I filed a Paypal claim as not received. Just as the thirty day mark was reached the bag showed up and turned out to be a very poor fake. I tried to modify my Paypal claim from not received to not as described, and they wouldn't let me. I spoke with someone on the telephone from Paypal and he told me there was a flaw in the Paypal protection system that you could only file a claim for one reason and in situations like mine to go to
eBay's buyer protection plan, which was still in place at the time, and which I did. Problem was, the buyer protection plan had a $35.00 processing fee. I got my money back, less shipping both ways and the $35.00, which amounted to almost $55.00. I contacted the seller and told her very plainly that selling counterfeit bags was illegal and that if she didn't refund the $55.00 I was still out that I was going to take her to small claims court, which I had every intention of doing. She paid the $55.00. She still came out on the good end because
eBay, not the seller, refunded the purchase price (less the fees). She ended up a few hundred dollars ahead. I watched her buying/selling on and off for a year and she had several none paying negatives, then eventually the id was no longer registered. Funny, her name was Brandy, same as the scammer in OK, but this one was in TN.