what to do if we are not getting any response from the client after the complition of order?

what to do if we are not getting any response from the client after the complition of order?

what if, client's forget to accept the order? 
in this case what to do? 
even i remind to my client frequently to accept (close/complete) the order.
but i did not get any reply from them..

kindly guide me for the same.. what to do..