Double billed

I've paid out 2 of my cellphone contracts in February in advance , knowingly that they will expire in June, so that I can cut out some expenses, ever since I've been billed those lines even after, I had payed them off, I've called vodacom several times and being told that my query has been escalated even this month, my bill still reflects the numbers that I had payed out in Feb. Honestly I'm do sick and tired of vodacom.