Product Authenticity complaints are among the most serious you can get, and will almost always get your account suspended. If you don't have multiple invoices (*NOT* receipts, such as what you'd get from liquidation sales or other forms of retail arbitrage, or purchases from either online or B&M stores) showing that you have bought that item from either the manufacturer or through their Authorized Distribution network, it's extremely unlikely that you'll be able to sell that item.
If you can't satisfy those requirements, you should create a removal order if you're selling FBA, to get your product back from the Amazon Fulfillment Centers. Then you'll want to DELETE the listing - Amazon may've removed your ability to sell it here, but it could still be showing as an inactive listing in your Inventory Manager screen, and that alone can get your account suspended if one of the bots roaming around looking for these type of violations stumbles across it.