Vodacom invoices incorrect

I am so tired and Vodacom and incorrect statements and invoices!! I have 3 Vodacom contracts. 2 of the contracts are combined on one invoice and the 3rd contract is on a separate invoice. Every single month i make an EFT payment with the amounts combined and i always round it off and pay R10 or more extra!! Now this is the 3rd month in a row where i get a call and sms from Vodacom saying i owe R180 and must select payment date before the 20th. How the HELL is this possible if i pay exactly what my invoices show ?????? This means YOUR invoices are then incorrect as the amounts reflecting on the invoice is always paid in full. I don't understand this. I am sick and tired of the same sh!@ every f!@$ing month!!! I have had enough of Vodacom and i will NOT renew any contract because of this!!!!! I am the client and I am correct! If my invoice shows an amount then that amount is paid so where the hell do you always get some amount from between 170 and 180 that is apparently outstanding. Because YOUR invoice is wrong then it is YOUR problem. I shouldn't be held responsible for this!! YOUR mistake NOT my problem!!! I refuse to pay anything NOT on my invoice. I expect this to be corrected immediately because according to the invoices i received i paid the correct amount. Sort this out on your side because i refuse to make any further payments!!!!!