Process improvement urgently needed!

We had two salespeople for some reason: as we selected the product and started negotiating, the salesperson said she was going to talk to someone else about our request, but instead, someone else was introduced to us, and that was the person who finalized our purchase. The biggest issue came after: that salesperson reviewed our invoice with us after it was paid for, and we left the store. Not even 5 minutes after, we got phone calls asking us to go back to the store because the pillows we had also purchased were not paid for - please keep in mind that at least 3 other people had reviewed that invoice. If one goes to a store and the store doesn't charge a customer for something, it shouldn't be the customer's fault to work around and fix the issue created by the store and its employees. PLEASE improve your process to have whoever saw the invoice and realized that the pillows were not paid for can review the invoices BEFORE the customer pays for their purchase. You have a beautiful store with great products, but clearly your sales and checkout processes need A LOT of improvement.