Answere phone but no nothing - hung up - received call at my business

I've been getting a lot of these types of calls lately. I guess they all graduated from Phone Scam College at the same time.
This one went to voicemail because I refuse to answer. Usually they hang up after one to three rings. Voicemail registered but no message. I blocked the number but they'll just call back on a different number.

I've also been getting a lot of calls that register as "Unknown" on the caller ID. Can't do anything about those.

If you want to block unknown calls download True Caller great program. You can block any number and it auto rejects unknown.

Is True Caller for cell phones? I use Phone tray for my lan line but looking for a good one to use for my cell phone.
Thanks.

Keep getting calls from this number. Don't know who this number bongs to nor do I know who they are.