On your mobile, when a caller has rung and appears in the log, right clicking it and adding it to the Reject list usuall does the trick. If they're already in your Contacts, the same applies.
On your landline, it's harder. Really serious nuisance calls can be reported to the police but they won't take much notice of a complaint about equally annoying Spam calls.
Wherever you are in the world will probably be different from here in England but I just bought a new handset and base unit which screens calls and it's so much quieter in here since. A call to your service provider might be worth a shot.