Call Blocking

We have had the same spam number call every single day for weeks on end. I have tried to use "Selective Call Rejection" to block it, but it still comes through. I have tried forwarding the spam calls. I can't use a third party app to help because they don't integrate with Comcast. It's obnoxious. Some days I receive 5+ spam calls. There has to be a better way to actually block these numbers.