SIM card problem after putting it in another iPhone

I recently upgraded to the new iPhone 6S so I was going to sell my 5S. I got it unlocked through AT&T, and I just wanted to test it before I shipped it to the buyer so I got the SIM card from my mom's 5S, which works on Verizon, and I put it in my old 5S. I set the phone up like it was new except for the activating cell service part, and everything worked fine. I put her SIM card back into her iPhone and now where it shows her phone number at the top of the contacts page, it has my name out beside there. It's my name, but her phone number. When I click on my name, it takes me to my contact info. Her iPad now states that it doesn't recognize her iPhone as well.

Did I mess something up by taking the SIM card out. How can I fix it?

Jessica