That is ridiculous. Your IP should have altered the figures before they were represented, and has put you in this situation - assuming that you had informed them about the increases.
I find it hard to believe that an IP would present an IVA proposal to creditors without verifying the information contained within it for accuracy, or that you would have signed a proposal knowing that you were paying higher figures which would affect your affordability.
I am afraid that the fact that you keep speaking to different people in the company, probably relates to the fact that you chose a large firm to represent you rather than a smaller specialist practice.
Regards, Melanie Giles, Insolvency Practitioner for over 20 years.
To have me propose an IVA for you, please visit:
http://www.melaniegiles.com/ivaEnquiry.asp
See customer feedback at:
http://www.iva.com/iva_companies/IVA_Advice_Bureau.asp