Customer service

I have just received an email stating that my son's education policy has been cancelled, I called the number on the letter ***, held the line for 40 minutes, spoke to Verna who told me that my policy has lapsed due to non-payment. My frustration is that I have 3 policies with Old mutual, the debit orders deduct on my payday, so how is it possible that there were no funds in my account and the other 2 policies went off successfully? I requested to speak to the manager and this guy refused, saying that the manager is going to tell me what he is telling me now. I do not understand, when my debit orders go off, there is always funds available. Please explain how this happened, there was not even a returned debit order to show that they tried deducting the monies.