Please don't chuck the wrongly prescribed insulin, nor give it back to pharmacy, as they'd have to chuck it.
Instead, please post to IDDT, who will send it to someone with diabetes in a developing country, where insulin is not easilt available and costs are way beyond what mpost people can afford. See
http://iddt.org/here-to-help/iddt-campaigning/iddt-campaigns-to-help-people-in-developing-countries Scroll down to section headed Collection of insulin and other supplies.