Upson is in A/P, and although he seems a nice guy, he has no control over the payment schedule. You need to talk to Martin, who is either the owner or his son...
They were chronically behind on payments when we dealt with them, but we had to ultimately make contact with their customer to get the money flowing that last time...
There were some rumours that one of their largest customers went bankrupt. MS is apparently trying to remedy all payables, in some cases offering payments monthly until full payment has been paid.