You need to understand how Comcast accounts are structured. It is predicated on the notion that there is a Primary, and up to 6 other people in the same household. Ergo the presumption of different names. It's structured based on presumed family usage since it's a residential account. I have my Primary and two secondaries in use right now. One is a minor variation of my name, and the other secondary is a nickname. Try doing that for a secondary account and see if it takes it for you. Use your first and middle initial instead of your full name or something like that. Maybe add a number to it. There's a lot of different ways you could go with this.
Also, if you are running a business, you need to look into a Comcast business class account.
Hello Sbateman13! Welcome to the Xfinity Forums. I'm glad you reached out to us with this issue.
Latoque has already given some great assistance! As they mentioned, you will need to have a slight variation to each username and the name it is associated with. Latoque also made a very good point that if you are using your services for business purposes, you may want to consider switching to a business class account. Let us know if this helps or if you have further questions.
Sbateman13, as I have not heard back from you in some time, I have closed this thread to further comments. I hope you were able to get this issue figured out with your usernames, but if you still need assistance, please feel free to start a new thread.