Scottish Power Problem? Have they removed money from my account?

TTmiles

Below you can see two screenshots I took of my Scottish Power online account.

The first one was taken when I logged into my Scottish Power internet account on 1/11/11 and the second was when I logged in again three days later on 4/11/11

The whole of my account history going back 6 months or more has changed.

NOTE: I'm not yet allowed to post links. Is there any way to upload the screenshots to show you?

My issue is this - and I should say I don't know if I'm losing my marbles - but I always thought a historical balance was FIXED.

So if I view my account on 1st november this year and it shows my balance on 15th July 2011 (for example) was £810.43 in credit then that's a fixed amount at that particular date right?

So how can I then log in on 4th November this year and find that my balance for 15th July 2011 has suddenly decreased to £525.92 in my online account?

How can a historical balance decrease?

I'm either missing something really obvious or something weird is going on with my account.

I've asked Scottish Power but they won't address the historical data, and keep saying it takes three days for a bill to change.

Even though the balance on more than one occasion changes when there's no bill for two weeks either side.

What am I missing?

Thanks

TT