My Local Ups Store Owes Me $676 For A Shipping Return Refund And Hasn't Paid Up After Over A Month Of Waiting. What Do I Do?

I 22M tried returning a very large package from a third party Amazon seller to the UPS store last month. I initially paid $676 for a shipping label to return the package and the seller told me after paying and filing a Amazon A to Z guarantee claim to return it through fed ex instead as the shipping would be cheaper. I ended up never shipping the box back through UPS but they have held my money hostage since then despite numerous attempts and phone calls in the past month to get refunded. Would it be worth my time and money to sue the UPS store in my area. I just want my money back because this is turning out to be a very stupid purchase that I made.

Edit: I currently live in Oklahoma so if I filed a small claims suit, it would have to be there