Pinnacle Financial Group - Know more about this collection agency

I got a call from Pinnacle Financial group today about an account I paid off three years ago. I stated that I would like to send them evidence of it being paid off by certified mail. I asked for the address and the collector began by asking for my address. I asked for theirs but she demanded I confirm mine first. I went ahead because I wasn't going to play their little game. She then began SPELLING out the company name. I informed her that I had a college degree and can spell, I just needed the address. She told me I had an attitude with her. I ALWAYS speak in a professional manner...it's required in my line of work. I politely asked for the address again. She told me again that if I was going to have an attitude with her, she was going to send my account back out into collections (!!!). I did not respond to her threat but merely asked her again, politely, for the address. She rattled it off quickly, but I'm a fast writer. I wish I had thought to record the conversation, but the answering machine is in another room.

I plan on sending off the envelope with a succinct letter to them about communicating with me. My need is two-fold: 1. How do I word a letter to them about this matter? and 2. Was her threat valid or should I report them to the proper governing authorities?

I've been having go-rounds with them over this account for two years. Two years ago, I mailed them a packet of information with the paid-in-full letter from my debt consolidation company who was handling my payments at the time, but I didn't do it certified with the return receipt. I will this time. I haven't checked my credit report, but is there a course of action I can take if they in fact have been reporting this account as delinquent even though it's been paid off?

Thanks in advance!