Hi Corry and welcome to the forum
If you guaranteed to make a specific dividend payment to creditors, and their claims have come in higher than had been originally anticipated, this could cause the need for additional payments. But you should ask your IP for the reasons why these are necessary, as this could also relate to higher fees as Ang has already mentioned.
Whilst this may be disappointing for you, after five years of payments, and extra four months is hardly a problem if this means that the balance of youe debts will be written off.
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