At the end of the day these people are just doing their job, trying to extract as much money as they can on the phone with you. I had one say to me, errr its bla from credit bla, do you have your debit card handy, as you need to pay £1300 to put your account in balance? (wow is that all, I dont think so?)
The most important thing to remember is dont be bullied. Tell them that you are aware of seriousness of the situation thats why you are taking out insolvency proceedings. That you are simply trying to communicate this to them in writing, via a professional to the big wigs, not verbally on the phone with them. Better not to waste your time with me and move on, as I cant pay. If you send someone round, I will ask them to leave and will refuse to speak to them. Be polite and professional, keep it short and to the point and hold your head up high.