Why have you not done this ? Has a review been conducted at all ? If your IP is doing their job correctly ( which it seems they are not) they will review the whole case before completion and, if your pay increased in previous years, but your IVA payment did not, they could ask you to play catch up. Alternatively, of course, they could continue to not do their job and just close anyway.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk