Drop them. At the start of this season a commercial account would pay by the 11th. Then each month a little later. Till it was the last day of service for Sept. I invoiced them for Sept on 9/26 and at the same time included a copy of Aug's invoice with past due written on it. 9/27 I got the check for August. Now next week will be the last service for Oct and they have not paid for Sept yet. Yes Invoices are dated due two weeks from sending them out. At this point I am thinking of dropping them before they get me for a bigger loss. I started with snow removal with them last winter. What good is charging them $200 to dig them out when they don't pay you.