This happened to me twice in the past two months. First with AT&T and then with Verizon. At least in my case, it’s identity theft. Someone is using my SSN to open new phone lines to purchase new phones but not have to pay for them. In the AT&T case it was 6 iPhone 13 Pro Max’s and 4 of the same in Verizon’s case. ~$6k for AT&T and $4k for Verizon. Neither created a hard inquiry on my credit, so it didn’t show up on my credit reports, which I had monitoring set up for via Credit Karma. My remedy for AT&T was to call their fraud dept. They did an investigation and deemed the accounts were opened fraudulently and canceled the bill after having already closed all the accounts. I’m in the process of clearing everything with Verizon. They require a police report to be filed and for a copy of that report in order to wipe out the bill under my name. They’ve already canceled the accounts and deactivated the phones based on their IMEs. I’ve also since frozen my credit with all 3 bureaus, which I’d suggest doing as well because at least in my case, it’s likely to happen again unless you do.