Note: this depends a lot on which governments you pay taxes to (country, state/province, city). With that in mind:
Check if there’s a “do not call” list where you live - i.e. a gov-enforced list of numbers that you are forbidden to call for advertisement. If there is one, put your number there.
Do not answer spam calls at all. Usually it’s easy to identify them, but there are some applications for this, like this (it’s in F-Droid so likely available for CalyxOS). By simply not answering those calls, your number gets marked as “inactive” by the advertisers/spammers/telemarketers, so the frequency of the calls gets lower over time.
Get a new phone number, redirect all legitimate contacts to your new number, and trash away the old one.