This is a problem I faced very early on, and caused me to close that telephone number because of the problems that arose. When I provided my voice line telephone number, I would get more than a dozen calls every day from scammers, and other criminals. They would offer to do web design or SEO services for me even though the domain already had content. Since I am on both the state, and national do not call list, these people were committing a crime by making unsolicited calls daily. This has went to the point of harassment, and since they changed their number that displays frequently, there was no way to block them without blocking all unknown callers.
Since I have a voicemail, I don’t get messages for web design and SEO services. If the criminal is calling the number, they are not leaving messages which means they know they are doing wrong. With that said, voicemail is the best solution. If it is a legitimate call, the caller will leave a voicemail message.