Changing from DLA to PIP first payment

Hi, I was originally receiving DLA (low rate care & high rate mobility), and had my care component paid to my bank account, I received my award letter from PIP stating that I was entitled to Standard rate Living component and Standard rate Mobility component from 29 July. My payment date for DLA was a Tuesday (every 4 weeks) and I received my last payment from them on 28 July for £65.40 which I presume is 3 weeks payment, my next payment from PIP was paid on 25 August for £296.62 which is £10.98 less than a 4 week payment, which I can't see why this has happened. I have phoned PIP on 27 Aug to ask for an explanation and they say I'm only entitled to 3 weeks and so many days, but I fail to see how this is, and they said they would get someone to call me back within 5 working days, I still have had no call back, or correspondence from PIP to clarify anything. I have phoned again to ask the same question, and I've been given the same response. It used to be that you would be notified of the amount of your first payment and the dates from & to, this hasn't happened ,and I've received nothing from DLA for my final payment either
Can anyone tell me are they correct? or am I entitled to the extra £10.98?

thanks for your reply, I thought I'd let you know, that I received my call back from PIP today, and the guy that phoned, has virtually said that there seems to be an error in the computer system set up, and that I would probably, he wouldn't commit to anything, receive the extra day with my next payment scheduled for 22 September, and if the extra day wasn't included I was to call back. He said he couldn't see what payment was being generated on the system because it was too far in advance.
I am also waiting on a mandatory reconsideration to be completed of my claim, and I've been told there is at least a 9 week waiting list for this (I've already waited approx. 6 weeks