These quick hang-ups are probably testing your number out to see of they get an answer. That way the can pass it on and try hitting you again.  Incredible all the calls I've gotten that come from numbers containing the exact final seven digits. I certainly am not going to answer a call with a zero in the fourth digit as it's an impossible number in the US. Scammers must not give much thought into the dummy numbers they use. Lots of them look ridiculous enough to stay away from.