Try squirting some geaphite lock lubricant into the lock... you really need
a new tumbler.
Second to last resort is get a new key from dealer... all they need is your
VIN number and proof of ownership. They have the key on record and they will
carve out a new key. Sometime, keys are so worn out that the lock does not
recognize it... or someone copied a worn key and makes the matter even
worse.
Last resort is let dealer drill out the lock and replace it with original
key code tumbler.