How difficult is it?

I have phoned Web Africa twice now to show them on a fault in their billing where they short charged me. The second time I advised that they have until end of day on Friday the 6th of Feb 2015 to send me an invoice, otherwise they will loose both my account and the amount short, since it wasted my time, which they are now responsible for the cost of my time and effort. I don't work for Web Africa, I'm a customer, so why should I do work for you and not get paid, so say goodbye to my business and to your outstanding amount. YOUR MISTAKE YOUR LOSS, you had two warnings to fix it and a week to react. Acc no VIA14