Bottom line is that, if the IVA is, indeed, in place, you are in a legally binding contract with your creditors and IP. You are free to rip this agreement up, but, then, the other parties are free to pursue you for their agreed compensations, possibly through the courts.
You state, "To my knowledge neither of my 2 creditors have been approached by IVA person on my behalf." --- Does this mean that the presentation of the proposal to creditors for the IVA hasn't actually taken place ? If this is so and that first payment you mention is merely an upfront, pre-agreement, payment, then you are not yet in an IVA and can cancel the creditors meeting and deal with creditors directly.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014