So after about 3-5 business days, the pending charges were returned (thankfully) and I gave it another try. 

It worked. So I guess it's one of those "system bugs" where it'll work when it WANTS to work. Just make sure to track your purchases so you aren't being charged for uncredited returns. Calling can only go so far because all phone support said was, "I assure you that your purchases has been successfully processed and the tax returns should be credited." That was false. But give it time and it'll fix itself.