Vodacom harassing me about an account I settled in April

I had a cellphone contract with Vodacom which I settled on the 7th of April. Now I am getting calls from Vodacom saying I am owing them R385. When I ask what this is this amount for the last agent said because my account is in arrears I then asked how and she said she was gonna transfer me to a relevant department I waited and I never got transferred she ended the call. This morning I got another call from Vodacom saying the same thing, the agent by the name of Simphiwe with the following call reference I ********** said this was a cancelation fee of which when I asked reasons behind the cancelation fee he then said he also doesn't know why he's just collecting what he sees reflecting on the system. My fear now is that Vodacom will blacklist me for the money I do not know as I called to settle this account and was never told about any cancelation fee. Please clear my name vodacom