Is there a way to add to customer's charge?

[SaskoDist]

I'm remote Retail, and a customer purchased 3 items from me, and while I was entering the items on my phone, a mistake was made, so I cleared the mistake, but didn't realized I have left one item off. So is there a way to recharge or add to their charge the missing item?  I don't even see a way to call them, as their phone number wasn't shown when I sent their receipt. This happened today. 

[VanKalkerFarms]

There is not a way to add items to a sale post completion of a transaction.  This would not be safe as anyone could make a sale the customer walk away and then the seller adds an additional item.