I’ve been using SaneBox for a couple of years, it works really well.
In the UK we have the “Corporate Telephone Preference Service” which you can sign up to for free, and you should not then receive cold calls. If one gets through I interrupt their opening spiel to tell them I am registered and so they should not be calling. They can be reported and fined. Otherwise try to have an underling answer all incoming calls and filter out the cold callers. I have someone that gives them very short shrift.
Why are you even on LinkedIn? If you’re running your own business surely you’re not still looking for a job.