Called and hung up instantly when I answered?

They call and don't leave a msg, I called back because I didn't know who it was and got an automated msg and quickly hung up. A few hours later they tried again.

A call from some insurance company which is very annoying.

very obviously an auto-dialler judging from the few seconds of silence before it diverted to a (suspiciously busy-sounding) call centre... couldn't be bothered waiting to hear why they were calling as I was at work.

telemarketing people for financial services, if your bank has sent you pamphlets for credit cards or insurance they call up to get you to buy.

Insurance and financial product marketing

They call and don't leave a message.

This is a annoying marketing service