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This is known as frostbite. The cold
has damaged your feet. If only the superficial layers (skin & fascia ) are damaged, it will get better it you keep your feet & body warm . So try doing that, by warm water (not too hot) and gentle application of a soothing ointment (calendula
) or petroleum jelly.
If there is no relief, see a doctor.
Please mention ur age and any other illness if you may have (like diabetes