Here contracts don't change within their validity. A change in a promotion/discount is fixed as per the signed/accepted contract, and if they change, they don't change without notifications and a confirmation from the customer of receiving that notification. Once the contract expires, the default case is disconnecting the service, unless specified otherwise in the contract.
As for payment thru bank transfer, it does not happen automatically unless decided in the contract by the customer. By default, it is payed manually. This means the bill can be checked thoroughly as usual. All bills can be checked electronically or by phone.
I thought the above was a norm all over the world.