I have a Quinny Zapp and have been really pleased with it. However, on Saturday, it decided not to fold down and then DH managed to fold it but now I can't open it. Anyone who has this, can you tell me if this is fixable? The two buttons on the side, one of them is jammed and it just won't budge!! Help? Making do with my Mothercare buggy which is fine for now, but prefer my Zapp.