Bad Service - Trying to cancel a contract coming to an end

I have a contract coming to an end and called Vodacom - because if you don't give them 30 days notice, it just continues. So I call them, and after entering numbers for various options, I eventually get hold of someone who then advised me that due to my account being in arrears (R100.88), I cannot cancel the contract. I then advise the consultant that the outstanding amount had been added to my invoice for the end of this month and that I was aware what it was for. She opens my account on her side and sees that the amount is not added to my invoice. Which basically means I cannot cancel this ONE contract (out of the many that I have) until the R100.88 is paid up. I then check my invoice and see that et voila! The R100.88 is indeed on my invoice! What did this consultant look at? Why did this consultant bother telling me what the total amount due was? I know what I pay Vodacom as I have been a client with them for more than 10 years. Be that as it may, I eventually get hold of the account department, tell them I made an immediate payment and can they please remove the R100.88 from my invoice as I really don't want to double pay them - especially not after this. Long story short - I have to phone them back in +-2 hours to cancel the contract. How nice