My factory unlocked iPhone 12 only accepts ATT???

I just received a new factory unlocked iPhone 12 from Apple but it only accepts ATT SIM cards. It isn’t acceptable with 4 different carriers that I’ve tried, straight talk and Verizon being two of them that works great in my rural area. The IMEI won’t work with anything but ATT!! (The worst carrier in my area!’) I’ve never had this problem with unlocked apple phones until now