unexplained high bill

Received sms saying phone has been softlocked. When I called the call centre they tell me I owe over R6000.00 which is impossible as I have top up contracts. For the month of June I was up to date with my payments yet my lines get cut. The lady at the call centre was so unhelpful. It was if my call was interrupting her. Lately this is the kind of service we get from vodacom. This has totally inconvenienced me as I use my phone for business. At this stage the offer from cell c sounds welcoming. I can't see how in 6 days my account can go up by R6000.00.