I had an account with T-Mobile a couple years ago. I had a line on the account for my mom. After her device (IPhone 8) was paid off, we went through the entire process of having the device unlocked. For several years since, she has used the unlocked device with a different SIM on a prepaid Walmart plan through Total Wireless. Recently, she switched service to Verizon. Her device showed as compatible, so she was sent a new SIM and had her prepaid service shut off. The new SIM however gives the message that the "sim is not supported". Verizon support says that her device is still locked by T-Mobile, and her settings do say it is sim locked.
I know the device was legitimately unlocked before, as she has been able to use it on a different carrier this whole time. I thought it was impossible to relock a phone?
When I left T-Mobile myself, they sent me a bill after my service was supposedly shut off. The billing cycle was after I had terminated service, so I refused to pay it. Obviously, this left my closed account in bad standing with them. I know this would impact getting a device unlocked now, but again, her device was paid off, unlocked, and used on another service years ago, long before I even left T-Mobile. Is there any way this could still somehow be the reason it is locked again?
I would really like to know if anyone else has had experience with a device that was definitely unlocked and used elsewhere, then shows as sim locked again, as even tech support told me they'd never heard of that happening.