I've just received an update text telling me that I have been awarded Mat Allowance but it's not the amount I was expecting at all, in fact it's half of the full entitlement which I earnt enough for in a 13 week test period on average. I started a new business in Jan last year (which was part of my test period) and it wasn't until the summer that I earnt enough for the full entitlement, I suspect that the NICs have something to do with it but I've always paid those fully despite not earning enough from my SE work to 'need' to and I was under the impression that I would be asked to pay the NICs from April 2018-April 2019 by HMRC before my claim was awarded (it says as much on the maternity allowance claim forms).
£72 per week, which was a weird number and I should be eligible for it all though. I eventually found that page (thank you for posting it!) and the reconsideration form says to call them first on the letter they will send me to confirm, so I'll give it a few days to come through and chat to them. I'm not panicking so much now as I was earlier as apparently they do this often!