URGENT: REFUSING TO CANCEL & SENDING WRONG INVOICES

I have paid the full cancellation amount as requested. My device is fully paid off and I have settled all dues. I have proof of payment. I visited the store today to finalize, yet I get messages saying 'not confirmed'. Furthermore, I called to cancel Insurance, they dropped my call and never called back. THEY HAVE EVEN SENT ME AN INVOICE FOR THIS MONTH DEMANDING MONEY. Why am I being billed when I PAID TO CANCEL? There is supposed to be no contract and no bill this month. I want EVERYTHING cancelled immediately: Contract, Insurance, Services. Stop billing me. If this is not fixed by tomorrow, I go to ICASA and Ombudsman.