It appears that you've been hit by two or three issues here.
Looking back at last year, I was only billed a small increase from my April bill onwards, no extra charges back to 31 March. Now, the first bill after the increase effectively adds the charges going back to the date of the increase + a month in advance at the higher rate. So, the bill is even higher than just the 'new' monthly price. OK, that generally makes sense to me - the increase is from a fixed date instead of the billing date.
However, it also appears that out-of-contract customers are seeing this increase applied from the 1 March, instead of the 31 March. I can't see this in the published terms and conditions, but it was announced on the EE newsroom site.
It seems like customers like me weren't told about that change. The billing system also seemed to be unaware and didn't increase the price on the March bill.
Instead of informing customers and waiving the charges out of goodwill (perhaps even legally), some April bills will likely consist of April-May charges at the higher rate + the higher charges for the early part of April + the price increase of £2.50 for the whole of March. By my reasoning, I'm expecting around £6 extra on the bill this month.
CS have told me to wait for my April bill to be produced before I can raise any query/complaint. But, I've already been told that it's 'in my terms and conditions'. I've hunted high and low and can't see it in the T+Cs though. And this extra money is going to be taken by direct debit regardless.
I'm collating as much information as I can from EE before the online documents get corrected and clarified. It's only £2.50 but contracts and consumer law are there for a reason.
