Here is an article I wrote for Cannabis Business Executive last year on this subject.  

https://www.cannabisbusinessexecutive.com/2017/06/five-signs-cannabis-customer-needs-placed-collection-agency/

Noramlly 60 days with no contact, no new orders and no promises to pay means that you need a colleciton agency. If you have any specific questions you can contact me at samf@agaltd.com