I have buy the stuff and already paid but after i paid 1 day

 the seller send me an email that my order is out of stock but in his sell page it show he have 2 left. So i ask for money back but no reply. I send again for cancel my transaction still no reply. What I should do to get my money back ?

The seller should have refunded your money right away.  Did you check your PayPal account to see if refunded?

If not, you can file an item not received case after the Estimated delivery date, but I bet the seller does refund you prior to that.