Unless you had IMMEDIATE PAYMENT REQUIRED, your buyer had four days to pay for his purchases.
On the fifth day, you can cancel the order, citing as the reason that the buyer didn't pay.
There is no need to contact buyer any more.
There is, however, a need for you to do more reading about a seller's options if a transaction goes wrong.
For starters, you need to lose your "do not accept returns" statement. If a buyer opens an item not as described case, you will be required to send the buyer a return label and to reimburse him in full upon receipt of returned item. Again, need to do more reading.
