My account with them is overdue

They send me a message that I owe them R1300 and they're going to deduct on 15th and I called one of their agent and she say they didn't take money from last month me I thought they my account was overdue in October so I throw away their sim in toilet in the middle of this week I called them where did money come from, they say is from last month and December month, and when I add this money is R199 + R199 I don't know about other money and I didn't use their airtime for this month, so please can you find out what all this money is all about help me to make them cancel this. Last month the money was in the bank they didn't take it so this month they say I owe them R1300 no they make me mad