Are you saying you can't even login to the control panel?
If you can, then just go to the domain registration section of the panel and if it says "yes" under the locked column, just click it and it will unlock it.
Unless you owe them money, I don't see why they'd put a registrar lock on it that you can't unlock yourself.
By DNS settings, you just mean the nameservers, right? Beyond that, I'm not sure that all settings are available if you don't also have an active hosting account.
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