Trying to ***** money from clients?

My usual monthly bill is R340, the annual network fee charged this year is R387.33 this equals R727.33, so please explain to my why the invoice I received for December is saying the payment due is R759.63? That's a small difference of R32.30, how this difference is my money not yours. I have all email correspondence as proof of what you said the annual radio fee is, so why are you trywto charge me more than your email said?

Please fix this urgently and send me an updated invoice for December