A woman from a bus company my group used LAST December calls insisting on payment for an invoice plus incurred interest from the person I replaced. Oddly enough, the call log showed she called Christmas Eve and the day after Christmas (perfect times to call and expect a fast response). I had an out of office voicemail on my phone saying I'd be back Monday to which this woman responds "If you don't call me back by Monday, I'll take you to collections."
I promptly return the call and ask her why is this the first I've heard of the issue. Had there been any correspondence by letter, or phone, I as M's replacement (the contact person for the invoice) would have been the person they reached. She admits they only faxed the bill but did so repeatedly to a now defunct e-fax number. I give her my new fax number and ask her to send me the invoice, but I also make sure to bring this to the attention of the guy who does the budgeting for our group. He says "Go on and pay it, but we shouldn't have to pay interest." To which I agree.
I had a feeling the next part was going to involve some ahem, heated discussion and went to an office so as not to distract anyone else. I call the vendor back and explain we're more than happy to cut a check but will only pay the principal amount and she loses it, starts screaming at me that "If you're at a restaurant and eat, you have to pay the bill!" To which I say "Well if you send it to the wrong table, I shouldn't be faulted." She finally said "Fine, pay the principal, do what you want!" and hung up on me.
Great way to do business, really.