Stupidest mistake I've ever made!

I am such an idiot I could shoot myself. Today I get something in the mail from the loan company for my new car. I was thinking maybe it was a check, that's what it looked like, haha. Instead it was a LATE NOTICE telling me that I didn't make my payment this month. I was looking at it thinking OH YES I DID!!! So I raced into the house and looked at my statement online. I see the payment, it was cashed on 8-13. So, I was like, yeah that's what I thought! So, I call the loan company and leave a message because they are already gone. I was like, "Hi, I received a late notice from you guys and on my bank statement it shows you cashed my check on 8-13." So, I began reading them everything on the check.."pay to the order of bla bla bla, for the amount of....wait a minute, I just said pay to the order of bla bla bla.....that's who my last car loan was through!!" "OMG!!!!! I paid the old loan company." My car has been paid off with them, my account is closed!!! HOLY SH%T. So, I call the place I DID PAY on accident and explain to the girl the problem and she said it's gonna take 21 business days before they will mail me a check. I am freaking out here. Who has an extra $421.00 to make a double payment because the first one went to the wrong person????? I am so pi$$ed at myself right now. I hope this doesn't show up as a late payment on my credit report!!!!!