Arrears Warning when Account is Not in Arrears

Nice one Vodacom. I pay according to the invoices and the statements that you send me. Last month I did as I usually do but then today I got a SMS saying I am in arrears. I checked my account and my bank account and paid according to the statement. I just found out that a charge was charged to my account on the 4th (not sure whether she said October or September), statement dated the 3rd September! How on earth can I be in arrears when I paid to your statement? R4600 was paid yet you hounding me over R100 that you suddenly charged to my account? Seriously?