Most of the big cell services have a spam mgmt offering now and I think it is no charge or minimal if any. They do a decent job of filtering out the obvious ones but the local spoofing calls will get through. Gets about 1/2 for me. Verizon has an interface that makes it very easy to block numbers as well. I catch a few more that way.
If they get through you need to do 1 of 2 things. Take the call and make sure there is an option to press a number to be removed from the list. If they don't offer that option you need to report them - again, Verizon offers a pretty simple interface to do that through. Not sure on the others.
Really important to do those items so that CAN-SPAM laws take effect on them. They are relying on you to not report them.
Oh, also do a search on CAN-SPAM and go to the govt registration site to register on the do-not-call list. Here is the link -
https://www.donotcall.gov/register/reg.aspx
Won't get them all but keeps it down considerably and only way we can push back against it.