(a) When any person has inadvertently used for an instrument chargeable with duty, a stamp of a description other than that prescribed for such instrument by the rules made under this Act, or a stamp of greater value than was necessary, or has inadvertently used any stamp for an instrument not chargeable with any duty; or

(b) when any stamp used for an instrument has been inadvertently rendered useless under section 15, owing to such instrument having been written in contravention of the provisions of section 13,