Accidental payments, how to reconcile?

Hi Guy's, 

I hope this is a simple one for the experienced :)

I have one customer who has paid me with no open invoice to them and another whom has paid 1 invoice twice. 

I am wondering the best way to record these so as I can reconcile the bank balance? 

For option 1 I was going to open an invoice then apply the payment, and then open a credit invoice to match to the refund payment. I am wondering if this is the correct way and/or if this affects my tax/income? 

For option 2 I was going to apply the 2nd payment to the same invoice then refund as a customer credit. 

Am I on the correct path or is there a more suitable way to process this? 

Many Thanks for your time :) Much Appreciated.