Demand money then ignore me!

On 6 Oct I received an SMS, phone call from Rene (which I missed) and an e-mail all demanding money. Each of them said Payment on your Trudon Ref is due (amount and reference given) but NO details whatsoever as to what money is due. I tried calling back 6 Oct and gave up after 10 minutes of waiting on the call. I have sent 3 e-mails to Rene and have cc'd in Trudon Customer Care on two of them and NOTHING! Not a word, not an e-mail, absolutely NOTHING!!!!! I am stilling waiting to find out WHAT I owe you money for?? As far as I can tell every invoice is paid timeously at the end of every month. If I have missed something, then I'm terribly sorry, but TELL ME!! DO NOT call me and demand money and then refuse to answer me! I WILL NOT accept that! A response would be very much appreciated! I have just tried calling again and after 10 minutes of waiting I got through to Shareen who put me through to Rene, at which stage I was cut off! ABSOLUTELY USELESS!!