I think you are very confused.

Asymmetric cryptography is a completely separate, much older technology that has nothing directly to do with cryptocurrencies.

Furthermore, Bitcoin does nothing to solve the kind of fraud problems you are talking about, and in fact makes the consequences of them much worse, since you no longer have a central authorities that can reverse fraudulant transactions and the like. The "double spend" problem refers to a problem in distributed systems, not applied security.