The buyer didn't pay the extra amount and offline, what should I do?

[zahid119]

I had a order with a buyer who asked additional work which will be compensated. Unfortunately, I didn't send order modification request at the spot and wanted him to pay in a new order after current order completes. The buyer was offline and 1st order was auto completed. He came back, saw the 1st order status and never accepted my second(extra payment) order in inbox. He's offline for weeks. What should I do ?