From the Terms & conditions
10.1 If we’re unsure of your credit history, we may ask you for a deposit or impose credit conditions. If you don’t pay this deposit or you break these conditions, we may:
(a) require you to make a payment to pay off any unpaid charges or to cover future charges;
(b) place, or change, a credit limit on your account; or
(c) suspend, restrict or disconnect your services.
10.2 We may keep your deposit until your agreement ends and may use it at any time to pay unpaid charges. We don’t pay interest on deposits.