Creditors will take a few weeks to catch up -- but you need not make any payments to them nor worry about interest being added. You just make the required payments to your IVA provider and abide by the agreed terms. You do not contact creditors, nor do they contact you.
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