demanding payment after receiving a zero balance statement

In October 2015 I was told by a call centre agent that my account will be paid up at the end of October 2015. I paid my normal amount and then stopped paying. A month or two ago I received notice from Hammond and Pole attorneys that I owe Vodacom About R2500.00. I queried this but firstly got no response from the attorneys. I am still waiting for a copy of a recording they made where a consultant acting on their behalf told me i was paid up. I agreed to pay them half the amount as full and final settlement and to stop them from instituting court proceedings. I wish, however that I could afford it to take them on in court, but I cant because very few normal people can take on a large company like Vodacom. I fail to understand why they demand money from me while I am in possession of a statement showing I overpaid. My account number with them QC282334