You should pay 10K that is your bill amount. 500 cashback will be added in next statement. So your next billed amount would be 500Rs less.
So in short you always have to pay what is mentioned as total due(total billed spend - previous cycle cashback). You don't have to perform any calculation they will do that for you.
Technically u can pay 9500 but its advisable to pay 10000 full to avoid any mess. U can decide depending on Amount. If it's very high than u can skip. Else better to pay it off.