@ValeriaV Hello, the fixed price deal you have fixes the cost per unit , but your bills will go up and down depending how many units you have actually used. It is like filling your car when the price per litre is fixed, but what you pay depends on how many litres you buy. Also your direct debit is worked out to give you enough money in your account to carry you through the expensive winter months, so it can be high in summer when you might think it should be lower.
@ValeriaV Scottish Power work out what they want your direct debit to be based on what they think your total usage will be over the entire year. Then they adjust your monthly payment accordingly so you're always in a healthy credit with them rather than a debit.
If you'd prefer to pay for what you've used, rather than what SP think you're going to use, you can switch to quarterly billing. Some people just transfer £100 or so from their bank current account into another bank account of their own each month, then pay the quarterly bill from that when it comes in. It's a little bit more expensive that way, but at least they always have control of their own money.
@ValeriaV If you look online you can see how much credit you have in your account, for example if you have £500 credit and your annual cost is £1000 then you have too much credit and the DD will be reduced until there is a correct amount for the winter months. Probably after a few months of £35 the DD will go up to £100 again. It is a nuisance because you do not know how much they will take. You could speak to customer services and ask for a DD that stays at the same value the whole year. Ring 0800 027 0072.
@ValeriaV You're right - the automatic changes are not good for a lot of people, but when you pay by DD there is no way around it. That's why if it's a serious concern for you, you would be better off changing to quarterly billing.
You use your gas and electric as normal, you don't pay anything monthly, but every three months you get a bill and only then do you pay it. If you save up what you would have paid monthly, you can use that to pay the three-monthly bill and have complete control of your own money. There is no DD, no changing amounts, and SP only get hold of your money once every three months, when you have a bill to pay..