jt,
This is an issue and one that all customers should be aware of.
A good way to avoid this is to ensure you are providing your supplier with regualr meter readings to ensure your bills are 'actual' and not 'estimated'.
Rather than phoning the supplier, which can be time consuming, customers can apply for an "online" tariff. These tariffs continue to offer the cheapest rates and enable customers to enter their 'actual' meter readings in to their online account. This reading is updated on your account within a few days and means that your payments should be accurate. NOTE: These tariffs are only available to customers willing to pay by Monthly Direct Debit.
Regards,
Scott Byrom
Utilities Manager
moneysupermarket.com