Abbey and a new biuld on a technicality

Japtastic_UK

After spending two hours on the phone to Abbey today and them asking the basic questions at the beginning apart from whether the house is a new build and I didn't realise it made a difference, they asked at the end at then decided they wanted another 5% so 20% instead of 15%, meaning another £11,400!! So annoying... So unless I can borrow this from the parents we are screwed, the thing that really puts the icing on the cake is that the house is actually just over a year old but the builder only put the completion cert in, in the last couple of weeks meaning it's technically brand new

Any way out of this if I can't find the extra cash considering the house is actually over a year old? Any way of proving this so they will accept?

Thanks