Eventually, the debtor runs out of ideas explaining why you haven't been paid or realizes you've exceeded your tolerance for listening to them. Repeated delays and broken promises to pay mean that the debtor is intentionally avoiding payment. Often, at this point, you won't be able to reach the debtor at all. He's on vacation with the Chief Financial Officer now. When communication breaks down with a company which owes your business money, you really have no choice but to hand the account over to a collection agency.
Collection attorneys are best of all, because they sue.
However, unless the overdue account is worth several thousands of dollars, a good collection attorney won't find it worth her time. They probably owe a bundle of money to many people. In this case, a bankruptcy may be their only option. In the event of bankruptcy, you must try to collect via the bankruptcy courts. You can't pursue independent paths of collection against the company.