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When a SIM card is blocked after multiple incorrect PIN attempts, the appropriate action is to request a Personal Unlock Key (PUK). The PUK is a security feature implemented by mobile network providers to protect users' SIM cards from unauthorized access. It is specifically designed to unlock a SIM that has been locked after entering the incorrect PIN multiple times.

The PUK consists of a unique code provided by the network operator when the SIM card is issued. Users can typically find this code on the original packaging of the SIM card or by contacting the network provider's customer service. Once the PUK is entered correctly, the user can reset their PIN and regain access to their SIM card.

Attempting more PIN guesses after a cooldown period may lead to further locking of the SIM card, making the situation worse. Contacting the device manufacturer for a reset code is also not viable, as the manufacturer does not manage SIM cards; this responsibility falls on the network provider. Gaining access through the network operator is a broader option and does not specifically address the immediate need to unlock the SIM card using the PUK.