S21 will not register to AT&T network after switching from Sprint and unable to retrieve voicemail

[sexyNMbabe]

My phone originally came from Samsung with Sprint sim card. I've since switched to AT&T. Now, I can't check my voicemail cause all my stuff is still trying to register under sprint....I'm not with SPRINT ANYMORE!! I've reset my phone numerous times...I'm at my wits end! 

[Je655]

I would recommend making sure your device is unlocked and if not submit a request for an unlock.

https://www.sprint.com/en/legal/unlocking-your-sprint-device.html

"Most mobile devices are programmed to prevent the device from operating with other wireless carriers’ networks without first being unlocked. We're committed to providing you with clear information about unlocking your mobile device.

If you purchased your device from Sprint, please follow the steps outlined below to determine your eligibility for device unlocking."

[sexyNMbabe]

It's unlocked. Sprint unlocked it so I could switch Sims. I bought it directly from Samsung

[Je655]

Have you tired dialing your own number? This brings me to my voicemail on t-mobile and Verizon.

[fungurl2010]

Go to boost store to fix it

[Fanboy2]

Go to the sprint/tmobile store and tell them to remove that lock