How to test USB to TTL cable is working
I have 2 exactly same cables which I have bought here, both work like a charm. Of course, that doesn't prove anything, but fake cables usually come from el'cheapo manufacturers who don't bother to replicate the exterior looks so precisely.

I wouldn't be surprised if your cable was not counterfeit, but simply defective, especially if it doesn't show up in device manager at all (does it?). Either way, time to open a dispute with the seller.