Unbelievable

According to my service provider Vodacom that there is a balance outstanding of R646 000 from this company and would like to understand from where is this coming from? I never signed any contract and thats why I have a prepaid phone. I don't even know the company. According to the records the your company are crediting my prepaid account with R55 each month, why? Your current usage is R0 and your outstanding balance is R646872.85. It will be deducted 2019-12-27. For more balances dial *135# free from your phone.