How to delete my phone number from ipod touch imessage settings

My son's ipod touch has my cell # listed as a way for the ipod touch to receive txt messages. It also has several of our email addresses. I have unchecked my phone number and email addresses from the list so he will not receive txts meant for my phone number an the other email addresses, but I want to delete my phone number from the list altogether. I am able to delete email addresses from the list, but my phone number does not have a symbol next to it to touch to delete, like the email addresses do. I can't figure out why my cell # is even on the list. It's not on my apple ID account. How do I take it off?

Thanks.