Can't add mobile phone to account - XFinity

I only have one phone - my cell phone. This appears on My Account/Settings as my preferred phone number. I wanted to set up text alerts, so it wants me to add my mobile number. When I try to do so, it tells me that number already exists on my account.

Edit: I entered this under the Customer Service forum, but the system moved it here. This is on the Xfinity/ My Account webiste, not mobile.

This question, "Can't add mobile phone to account," is about XFinity-Comcast TV Television Apps.

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