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This might be a case of Portforwarding issue. If you have set port mapping rules to the modem previously and just recently reset your modem, then that could be the reason why it's no longer working at this point.
If in the event that you haven't saved any portforwarding settings in the modem, then as a last resort, you may want to reset your modem first and see how it goes. If it still fails, you may need to open the specific port numbers for FTP transfer.
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