Ignoring all the other issues, you can't even be following the code you wrote. You don't keep track of who has paid for what unless the transaction has hit the blockchain, each page refresh you throw everything away. This is unworkable as any form of payment system.

yes i know. refreshing the page will send post request again and generate other receiving address. which i want to avoid thats why am just looking for other way. but other issues are not big issue as this is just a sample script. can be implemented

my problem is only that. to avoid refreshing the page. i may find myself using ajax with loading gif to determine payment if received. but i didn't want to use ajax

This doesn't address the problems discussed. Simple as you think, this isn't a viable payment script, you literally don't track anything until a transaction is confirmed on the blockchain (ignoring all other issues already mentioned associated with this).