Called to say I owe, but nothing owing

Good day. Yesterday I received a computerised call from Vodacom stating that I had not paid my account of R3900 and I should pay within 24 hours to prevent further action. My Vodacom account is paid via debit order. I went to the Vodacom Branch this morning and they confirmed that there is no outstanding funds on my account. Why do you contact your customers and threaten them when my account is in order. I have been a Vodacom customer for many years and do not feel that this is the manner in which I should be treated.