Scammers can fake their 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.
Comcast won't let you block your own number, so there's nothing you can do without resorting to 3rd party hardware.
I can tell you that I have had similar instances of this occurring on both my cellular phone and home phone. There seems to be a "spoofing" scam where fraudsters are using your own number to call you and others. The FTC has a a fantastic article about these type of calls and the actions that you can do to protect yourself (article found here: https://www.consumer.ftc.gov/blog/2015/07/getting-calls-your-own-number). Per that article: "Bottom line? These calls from your own number are illegal. Don’t pick up — or press buttons to be taken off the call list or to talk to a live person. That just leads to more calls. It’s best to ignore them, and move on with your day." Unfortunately Comcast cannot stop these actions from happening, but we do have some calling features that can help to combat these type of unwanted calls. For Xfinity Home Phones To Activate Call Screening Lift the receiver and listen for the dial tone. Press *60. Follow the prompts to activate the feature and to add, delete or review the numbers on your list. When creating your list, include the area code for local and long distance numbers. To block calls from the last number that called you, press # when prompted. (More details about stopping unwanted calls can be found here: https://forums.xfinity.com/t5/Phone/ANSWERED-How-to-stop-unwanted-calls/ta-p/3170369) For Xfinity Cell Phones Blocking numbers on iPhones Go to your Phone icon. If you've saved the number in your phone, go to the contact and scroll down to select "Block this Caller." If the number is in your recent calls, select the blue "i" icon and scroll down to select "Block this Caller." Blocking numbers on Android phones Go to your Phone icon. Go to your recent calls, or your contacts list if you've saved the number already. Depending on which Android phone you have, select More, Details, or an icon with three vertical dots. Then, select Block. We also always recommend that you report these type of calls (every instance) to the FTC and/or FCC; their information can be found in the article listed above.