I work for an ASX top 20 company and I hate to say that we...

I work for an ASX top 20 company and I hate to say that we worked with a service provider in November last year with payment due in March 2015. They are still awaiting payment. We have had issues (which are not uncommon) in our accounts payable. In order to keep our business they have continued to work without pay and are onto phase 2 and still awaiting payment.
I have seen this happen often. Invoices get lost, someone who has to sign off is away, accounts payable make a mistake, tracking numbers don't match, mistakes in invoice amounts etc etc.
The point is, it would be foolish for us to look at one line item and guess who has paid what as some of these things take a long time and seldom arrive when they should.