Since Comcast won't let you block your own number, there's nothing you can do without resorting to 3rd party hardware. Scammers don't need to "clone" the phone, they can just fake the caller ID info, and using the number they're calling seems to be a popular trick. For more information see any of the many article links at https://www.google.com/search?q=caller+id+my+own+number, for example https://www.consumer.ftc.gov/blog/getting-calls-your-own-number.
Welcome to the forums.The information provided by @BruceW is correct. Let us know if there's anything else we can assist you with.