Is taking prescription sunglasses from a medical insurance company, after the company initially refused but then it became clear there was an agreement allowing it, unlawful (haram), and what should I do with them if it is unlawful?

If the branch that made the glasses confirmed that there is an agreement with the medical insurance company and that the amount is allocated to you, then there is no harm in you keeping the glasses and using them. It is advisable to ask about the ruling on matters before undertaking them, based on the Almighty's saying: ﴿So ask the people of the Reminder if you do not know.﴾