I need a document confirming that the phone is linked to the operator, or unlocking the phone

Good afternoon. The fact is that I bought a phone from a store called stoxx, bought a phone that was not linked to the operator (unlocked), sent a blocked one, now they are asking for proof that this phone is blocked by the operator. Because I am in another country (Europe, Belarus), there are no official apple services here. Please help in this matter or maybe please help to unblock it.

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