-Not a Drop Shipping store-
I accidently shipped the wrong item to my customer.
My customer ordered a $100 item, and I accidently sent them a completely different item, but it has a higher value of $300.
The customer noticed the mistake, and contacted us first, and we quickly replied, apologized, and sent them a pre-paid return shipping label.
Now 5 days later after sending a pre-paid return label, they never shipped it back, I assumed they realized it has a higher value, and hasn't replied to emails / phone calls.
What should we do?