Account settlement

I recently settled my cellphone contract with Vodacom in December last year but I just received a statement from them saying due amount for this month R380 but the account was settled i don't understand how i owe them when I am no longer using their cellphone contract .they cancelled everything immediately when I settled the account so how is it possible that I owe them and their consultant are so *********** its like they are not trained properly because each constant tells me different story when I ask what is going on