Incorrect billing?

I have just received a billing update. It appears that I am about £700 in debit.
For gas and electricity.
The statement says that on the 25/4/2019
I had 6 bill amendments totalling approximately this amount £700.
I had smart meters installed this year now I am worried that this the Npower debacle happening again. Before smart meters I had always sent Bulb my readings no problems.
Something has really gone wrong I know That I hadn’t used this much gas and electricity.
My house had been empty for most of December 2018.
Plus I don’t think energy companies can bill you for previous years.