I can feel your sadness. It happened with me as well where buyer lates delivery by non responsive cooperation.
Its situation where your hands are tied.
If you cancel order, order completion rate effects and if you wait, order on-time delivery rate effects.
In both conditions, level is gone.
When buyer is offline, I usually hit delivery by saying "delivering work, due to lack of response".
And this method is working to put pressure on client to respond. Else order marked complete in 3 days.
For now, I suggest you spent more hard work this month with more orders with great pace.
Level is updated every month, so hope you get back your level next month.