I could not say for certain, but, playing devil's advocate: The secured loan repayments would have been allowed as an expense in your I&E, so denying this amount to creditors as part of your disposable income. Had interest not been over-charged on the loan, these repayments would have been lower and, therefore, your disposable income and, by extension, your IVA payment, would have been higher. So, arguably, at least some of this repayment coveing those payments made during the IVA, should be paid back to the creditors.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014