Contact your IP directly, making a formal complaint, as whoever you are speaking to seems to still have no interest in even explaining the figures to you. Complain by email and also by registered post, keeping copies. If the IP is of no help, you can escalate the complaint to their regulatory body.
Even if the IP is in the right, or believes he is, he should, at the least, explain his reasoning to you.
The RB will not intervene directly, but could, if they agree with your complaint, fine the IP and, sometimes, this possibility makes the IP think twice.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014