Blocked iPhone

Hello! My mom bought a new SIM card, inserted it into the iPhone and it got blocked. The message on the screen says “SIM card is invalid. The SIM card inserted in this iPhone belongs to a cellular operator that is not supported by the current policy on the activation server. The problem you encountered is not related to the iPhone hardware. Insert a different SIM card from a supported cellular carrier, or have them unlock this iPhone. Contact Apple for details.“ I talked to cellular carrier, they said they can’t to anything.