Unhappy Client

I have an issue with Vodacom. I had a data contract with them and I did an early cancellation which I was sent a quote with an amount to pay for them to cancel my data contract, I paid the amount and sent them proof of payment together with a copy of my ID and signed quotation. that was in April. I'm still receiving invoices that I owe R404 which no one can explain to me where does it come from after I have cancelled the contract with them.

I've been to the Vodacom store, they couldn't explain and instead they gave me a number I can call which I did and I've been sent from pillar to post.