said by Chris w :Thanks, I think the device is useless...
No, just locked to prevent end users/customers from making any changes.
Did you contact your ISP support and ask them to make the wanted changes for you? You should refer to your ISP Terms and Use Agreements. Do you own the Modem or are you renting it or is it a loaner unit from your ISP? Depending on whether you own it and paid for it, then you can use that to request that they unlock the unit for you to administer.