Hi Wendy
Do not worry, these people are paid to stress a payment out of you, you have not done anything wrong, you are, trying to address your debt and that is a good thing. You may get calls for a while, it takes time to filter down to the bods on phone duty, simply tell them that you are proposing an IVA and dont let them say anything, write it down if you need to, tell them the name of your IP etc and tell them to please update their records. Speak calmly and politely and then put the phone down. If they interupt you tell them that they have made their position clear, and to let you do the same. Or as Neverending says, phone them first so that they have something on screen for each day. You have nothing to be ashamed of.
Good luck with it all
LILY