Billing calculation query since smart meter

I Wish I had never bothered having one installed.
Ok so joined in July, first bill August then September. All good. Had the meters installed 27th September. No money taken October, it took until the 7th November to finally get someone to sort it. Bill done. Was informed would be as usual from December.
11th November had a new bill. Previous bills credited then difference between august and 11th November charged. Ok. Bill would be as normal December I was told.
This morning I find I have used £400 of energy. Not what you want to see on bleary opening eyes at 7am. Panic over. They have credited bills since August and then taken it with today’s in one lump sum.
Is this going to be my life now? I know how much I am paying monthly. I know how much I have in credit until they bill. Are they going to keep crediting and taking as a huge lump monthly? Because what I don’t know is how much I have actually used in cost this month to know if I should be topping it up a little. My monthly payment is still the same although I’m going to have to alter my billing date as the bill for some reason comes out before the payment does as it seems to get later every month.
I’m seriously considering changing again. Customer service is terrible and unless you use a lot of energy and need to know where to cut back, smart meters don’t help. They just keep flashing and you feel like turning everything off and sitting in the cold and dark in case you’re using a lot. Especially when you have this sort of billing. My credit is going down rapidly. I thought the whole reason for paying a monthly set price meant winter took credit you built up. But I can’t plan with this billing.